Calculus Examples

$f (x) = 8 x^{8} {(5 - x)}^{7}$

Step 1

Find the first derivative of the function.

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Step 1.1

Since $8$ is constant with respect to $x$ , the derivative of $8 x^{8} {(5 - x)}^{7}$ with respect to $x$ is $8 \frac{d}{d x} [x^{8} {(5 - x)}^{7}]$ .

$8 \frac{d}{d x} [x^{8} {(5 - x)}^{7}]$

Step 1.2

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = x^{8}$ and $g (x) = {(5 - x)}^{7}$ .

$8 (x^{8} \frac{d}{d x} [{(5 - x)}^{7}] + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 1.3

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = x^{7}$ and $g (x) = 5 - x$ .

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Step 1.3.1

To apply the Chain Rule, set $u$ as $5 - x$ .

$8 (x^{8} (\frac{d}{d u} [u^{7}] \frac{d}{d x} [5 - x]) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 1.3.2

Differentiate using the Power Rule which states that $\frac{d}{d u} [u^{n}]$ is $n u^{n - 1}$ where $n = 7$ .

$8 (x^{8} (7 u^{6} \frac{d}{d x} [5 - x]) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 1.3.3

Replace all occurrences of $u$ with $5 - x$ .

$8 (x^{8} (7 {(5 - x)}^{6} \frac{d}{d x} [5 - x]) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 1.4

Differentiate.

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Step 1.4.1

By the Sum Rule, the derivative of $5 - x$ with respect to $x$ is $\frac{d}{d x} [5] + \frac{d}{d x} [- x]$ .

$8 (x^{8} (7 {(5 - x)}^{6} (\frac{d}{d x} [5] + \frac{d}{d x} [- x])) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 1.4.2

Since $5$ is constant with respect to $x$ , the derivative of $5$ with respect to $x$ is $0$ .

$8 (x^{8} (7 {(5 - x)}^{6} (0 + \frac{d}{d x} [- x])) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 1.4.3

Add $0$ and $\frac{d}{d x} [- x]$ .

$8 (x^{8} (7 {(5 - x)}^{6} \frac{d}{d x} [- x]) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 1.4.4

Since $- 1$ is constant with respect to $x$ , the derivative of $- x$ with respect to $x$ is $- \frac{d}{d x} [x]$ .

$8 (x^{8} (7 {(5 - x)}^{6} (- \frac{d}{d x} [x])) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 1.4.5

Multiply $- 1$ by $7$ .

$8 (x^{8} (- 7 {(5 - x)}^{6} \frac{d}{d x} [x]) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 1.4.6

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$8 (x^{8} (- 7 {(5 - x)}^{6} \cdot 1) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 1.4.7

Multiply $- 7$ by $1$ .

$8 (x^{8} (- 7 {(5 - x)}^{6}) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 1.4.8

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 8$ .

$8 (x^{8} (- 7 {(5 - x)}^{6}) + {(5 - x)}^{7} (8 x^{7}))$

Step 1.4.9

Move $8$ to the left of ${(5 - x)}^{7}$ .

$8 (x^{8} (- 7 {(5 - x)}^{6}) + 8 \cdot {(5 - x)}^{7} x^{7})$

Step 1.5

Simplify.

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Step 1.5.1

Apply the distributive property.

$8 (x^{8} (- 7 {(5 - x)}^{6})) + 8 (8 {(5 - x)}^{7} x^{7})$

Step 1.5.2

Multiply $- 7$ by $8$ .

$- 56 (x^{8} ({(5 - x)}^{6})) + 8 (8 {(5 - x)}^{7} x^{7})$

Step 1.5.3

Multiply $8$ by $8$ .

$- 56 x^{8} {(5 - x)}^{6} + 64 ({(5 - x)}^{7} x^{7})$

Step 1.5.4

Factor $8 x^{7} {(5 - x)}^{6}$ out of $- 56 x^{8} {(5 - x)}^{6} + 64 {(5 - x)}^{7} x^{7}$ .

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Step 1.5.4.1

Factor $8 x^{7} {(5 - x)}^{6}$ out of $- 56 x^{8} {(5 - x)}^{6}$ .

$8 x^{7} {(5 - x)}^{6} (- 7 x) + 64 {(5 - x)}^{7} x^{7}$

Step 1.5.4.2

Factor $8 x^{7} {(5 - x)}^{6}$ out of $64 {(5 - x)}^{7} x^{7}$ .

$8 x^{7} {(5 - x)}^{6} (- 7 x) + 8 x^{7} {(5 - x)}^{6} (8 (5 - x))$

Step 1.5.4.3

Factor $8 x^{7} {(5 - x)}^{6}$ out of $8 x^{7} {(5 - x)}^{6} (- 7 x) + 8 x^{7} {(5 - x)}^{6} (8 (5 - x))$ .

$8 x^{7} {(5 - x)}^{6} (- 7 x + 8 (5 - x))$

Step 2

Find the second derivative of the function.

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Step 2.1

Differentiate using the Constant Multiple Rule.

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Step 2.1.1

Simplify each term.

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Step 2.1.1.1

Apply the distributive property.

$f'' (x) = \frac{d}{d x} (8 x^{7} {(5 - x)}^{6} (- 7 x + 8 \cdot 5 + 8 (- x)))$

Step 2.1.1.2

Multiply $8$ by $5$ .

$f'' (x) = \frac{d}{d x} (8 x^{7} {(5 - x)}^{6} (- 7 x + 40 + 8 (- x)))$

Step 2.1.1.3

Multiply $- 1$ by $8$ .

$f'' (x) = \frac{d}{d x} (8 x^{7} {(5 - x)}^{6} (- 7 x + 40 - 8 x))$

Step 2.1.2

Subtract $8 x$ from $- 7 x$ .

$f'' (x) = \frac{d}{d x} (8 x^{7} {(5 - x)}^{6} (- 15 x + 40))$

Step 2.1.3

Since $8$ is constant with respect to $x$ , the derivative of $8 x^{7} {(5 - x)}^{6} (- 15 x + 40)$ with respect to $x$ is $8 \frac{d}{d x} [x^{7} {(5 - x)}^{6} (- 15 x + 40)]$ .

$f'' (x) = 8 \frac{d}{d x} (x^{7} {(5 - x)}^{6} (- 15 x + 40))$

Step 2.2

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = x^{7} {(5 - x)}^{6}$ and $g (x) = - 15 x + 40$ .

$f'' (x) = 8 (x^{7} {(5 - x)}^{6} \frac{d}{d x} (- 15 x + 40) + (- 15 x + 40) \frac{d}{d x} (x^{7} {(5 - x)}^{6}))$

Step 2.3

Differentiate.

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Step 2.3.1

By the Sum Rule, the derivative of $- 15 x + 40$ with respect to $x$ is $\frac{d}{d x} [- 15 x] + \frac{d}{d x} [40]$ .

$f'' (x) = 8 (x^{7} {(5 - x)}^{6} (\frac{d}{d x} (- 15 x) + \frac{d}{d x} (40)) + (- 15 x + 40) \frac{d}{d x} (x^{7} {(5 - x)}^{6}))$

Step 2.3.2

Since $- 15$ is constant with respect to $x$ , the derivative of $- 15 x$ with respect to $x$ is $- 15 \frac{d}{d x} [x]$ .

$f'' (x) = 8 (x^{7} {(5 - x)}^{6} (- 15 \frac{d}{d x} x + \frac{d}{d x} (40)) + (- 15 x + 40) \frac{d}{d x} (x^{7} {(5 - x)}^{6}))$

Step 2.3.3

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$f'' (x) = 8 (x^{7} {(5 - x)}^{6} (- 15 \cdot 1 + \frac{d}{d x} (40)) + (- 15 x + 40) \frac{d}{d x} (x^{7} {(5 - x)}^{6}))$

Step 2.3.4

Multiply $- 15$ by $1$ .

$f'' (x) = 8 (x^{7} {(5 - x)}^{6} (- 15 + \frac{d}{d x} (40)) + (- 15 x + 40) \frac{d}{d x} (x^{7} {(5 - x)}^{6}))$

Step 2.3.5

Since $40$ is constant with respect to $x$ , the derivative of $40$ with respect to $x$ is $0$ .

$f'' (x) = 8 (x^{7} {(5 - x)}^{6} (- 15 + 0) + (- 15 x + 40) \frac{d}{d x} (x^{7} {(5 - x)}^{6}))$

Step 2.3.6

Simplify the expression.

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Step 2.3.6.1

Add $- 15$ and $0$ .

$f'' (x) = 8 (x^{7} {(5 - x)}^{6} \cdot - 15 + (- 15 x + 40) \frac{d}{d x} (x^{7} {(5 - x)}^{6}))$

Step 2.3.6.2

Move $- 15$ to the left of $x^{7} {(5 - x)}^{6}$ .

$f'' (x) = 8 (- 15 \cdot (x^{7} {(5 - x)}^{6}) + (- 15 x + 40) \frac{d}{d x} (x^{7} {(5 - x)}^{6}))$

Step 2.4

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = x^{7}$ and $g (x) = {(5 - x)}^{6}$ .

$f'' (x) = 8 (- 15 x^{7} {(5 - x)}^{6} + (- 15 x + 40) (x^{7} \frac{d}{d x} ({(5 - x)}^{6}) + {(5 - x)}^{6} \frac{d}{d x} (x^{7})))$

Step 2.5

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = x^{6}$ and $g (x) = 5 - x$ .

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Step 2.5.1

To apply the Chain Rule, set $u$ as $5 - x$ .

$f'' (x) = 8 (- 15 x^{7} {(5 - x)}^{6} + (- 15 x + 40) (x^{7} (\frac{d}{d u} (u^{6}) \frac{d}{d x} (5 - x)) + {(5 - x)}^{6} \frac{d}{d x} (x^{7})))$

Step 2.5.2

Differentiate using the Power Rule which states that $\frac{d}{d u} [u^{n}]$ is $n u^{n - 1}$ where $n = 6$ .

$f'' (x) = 8 (- 15 x^{7} {(5 - x)}^{6} + (- 15 x + 40) (x^{7} (6 u^{5} \frac{d}{d x} (5 - x)) + {(5 - x)}^{6} \frac{d}{d x} (x^{7})))$

Step 2.5.3

Replace all occurrences of $u$ with $5 - x$ .

$f'' (x) = 8 (- 15 x^{7} {(5 - x)}^{6} + (- 15 x + 40) (x^{7} (6 {(5 - x)}^{5} \frac{d}{d x} (5 - x)) + {(5 - x)}^{6} \frac{d}{d x} (x^{7})))$

Step 2.6

Differentiate.

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Step 2.6.1

By the Sum Rule, the derivative of $5 - x$ with respect to $x$ is $\frac{d}{d x} [5] + \frac{d}{d x} [- x]$ .

$f'' (x) = 8 (- 15 x^{7} {(5 - x)}^{6} + (- 15 x + 40) (x^{7} (6 {(5 - x)}^{5} (\frac{d}{d x} (5) + \frac{d}{d x} (- x))) + {(5 - x)}^{6} \frac{d}{d x} (x^{7})))$

Step 2.6.2

Since $5$ is constant with respect to $x$ , the derivative of $5$ with respect to $x$ is $0$ .

$f'' (x) = 8 (- 15 x^{7} {(5 - x)}^{6} + (- 15 x + 40) (x^{7} (6 {(5 - x)}^{5} (0 + \frac{d}{d x} (- x))) + {(5 - x)}^{6} \frac{d}{d x} (x^{7})))$

Step 2.6.3

Add $0$ and $\frac{d}{d x} [- x]$ .

$f'' (x) = 8 (- 15 x^{7} {(5 - x)}^{6} + (- 15 x + 40) (x^{7} (6 {(5 - x)}^{5} \frac{d}{d x} (- x)) + {(5 - x)}^{6} \frac{d}{d x} (x^{7})))$

Step 2.6.4

Since $- 1$ is constant with respect to $x$ , the derivative of $- x$ with respect to $x$ is $- \frac{d}{d x} [x]$ .

$f'' (x) = 8 (- 15 x^{7} {(5 - x)}^{6} + (- 15 x + 40) (x^{7} (6 {(5 - x)}^{5} (- \frac{d}{d x} x)) + {(5 - x)}^{6} \frac{d}{d x} (x^{7})))$

Step 2.6.5

Multiply $- 1$ by $6$ .

$f'' (x) = 8 (- 15 x^{7} {(5 - x)}^{6} + (- 15 x + 40) (x^{7} (- 6 {(5 - x)}^{5} \frac{d}{d x} x) + {(5 - x)}^{6} \frac{d}{d x} (x^{7})))$

Step 2.6.6

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$f'' (x) = 8 (- 15 x^{7} {(5 - x)}^{6} + (- 15 x + 40) (x^{7} (- 6 {(5 - x)}^{5} \cdot 1) + {(5 - x)}^{6} \frac{d}{d x} (x^{7})))$

Step 2.6.7

Multiply $- 6$ by $1$ .

$f'' (x) = 8 (- 15 x^{7} {(5 - x)}^{6} + (- 15 x + 40) (x^{7} (- 6 {(5 - x)}^{5}) + {(5 - x)}^{6} \frac{d}{d x} (x^{7})))$

Step 2.6.8

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 7$ .

$f'' (x) = 8 (- 15 x^{7} {(5 - x)}^{6} + (- 15 x + 40) (x^{7} (- 6 {(5 - x)}^{5}) + {(5 - x)}^{6} (7 x^{6})))$

Step 2.6.9

Move $7$ to the left of ${(5 - x)}^{6}$ .

$f'' (x) = 8 (- 15 x^{7} {(5 - x)}^{6} + (- 15 x + 40) (x^{7} (- 6 {(5 - x)}^{5}) + 7 \cdot ({(5 - x)}^{6} x^{6})))$

$f'' (x) = 8 (- 15 x^{7} {(5 - x)}^{6} + (- 15 x + 40) (x^{7} (- 6 {(5 - x)}^{5}) + 7 {(5 - x)}^{6} x^{6}))$

Step 3

To find the local maximum and minimum values of the function, set the derivative equal to $0$ and solve.

$8 x^{7} {(5 - x)}^{6} (- 7 x + 8 (5 - x)) = 0$

Step 4

Find the first derivative.

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Step 4.1

Find the first derivative.

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Step 4.1.1

Since $8$ is constant with respect to $x$ , the derivative of $8 x^{8} {(5 - x)}^{7}$ with respect to $x$ is $8 \frac{d}{d x} [x^{8} {(5 - x)}^{7}]$ .

$8 \frac{d}{d x} [x^{8} {(5 - x)}^{7}]$

Step 4.1.2

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = x^{8}$ and $g (x) = {(5 - x)}^{7}$ .

$8 (x^{8} \frac{d}{d x} [{(5 - x)}^{7}] + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 4.1.3

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = x^{7}$ and $g (x) = 5 - x$ .

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Step 4.1.3.1

To apply the Chain Rule, set $u$ as $5 - x$ .

$8 (x^{8} (\frac{d}{d u} [u^{7}] \frac{d}{d x} [5 - x]) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 4.1.3.2

Differentiate using the Power Rule which states that $\frac{d}{d u} [u^{n}]$ is $n u^{n - 1}$ where $n = 7$ .

$8 (x^{8} (7 u^{6} \frac{d}{d x} [5 - x]) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 4.1.3.3

Replace all occurrences of $u$ with $5 - x$ .

$8 (x^{8} (7 {(5 - x)}^{6} \frac{d}{d x} [5 - x]) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 4.1.4

Differentiate.

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Step 4.1.4.1

By the Sum Rule, the derivative of $5 - x$ with respect to $x$ is $\frac{d}{d x} [5] + \frac{d}{d x} [- x]$ .

$8 (x^{8} (7 {(5 - x)}^{6} (\frac{d}{d x} [5] + \frac{d}{d x} [- x])) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 4.1.4.2

Since $5$ is constant with respect to $x$ , the derivative of $5$ with respect to $x$ is $0$ .

$8 (x^{8} (7 {(5 - x)}^{6} (0 + \frac{d}{d x} [- x])) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 4.1.4.3

Add $0$ and $\frac{d}{d x} [- x]$ .

$8 (x^{8} (7 {(5 - x)}^{6} \frac{d}{d x} [- x]) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 4.1.4.4

Since $- 1$ is constant with respect to $x$ , the derivative of $- x$ with respect to $x$ is $- \frac{d}{d x} [x]$ .

$8 (x^{8} (7 {(5 - x)}^{6} (- \frac{d}{d x} [x])) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 4.1.4.5

Multiply $- 1$ by $7$ .

$8 (x^{8} (- 7 {(5 - x)}^{6} \frac{d}{d x} [x]) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 4.1.4.6

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$8 (x^{8} (- 7 {(5 - x)}^{6} \cdot 1) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 4.1.4.7

Multiply $- 7$ by $1$ .

$8 (x^{8} (- 7 {(5 - x)}^{6}) + {(5 - x)}^{7} \frac{d}{d x} [x^{8}])$

Step 4.1.4.8

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 8$ .

$8 (x^{8} (- 7 {(5 - x)}^{6}) + {(5 - x)}^{7} (8 x^{7}))$

Step 4.1.4.9

Move $8$ to the left of ${(5 - x)}^{7}$ .

$8 (x^{8} (- 7 {(5 - x)}^{6}) + 8 \cdot {(5 - x)}^{7} x^{7})$

Step 4.1.5

Simplify.

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Step 4.1.5.1

Apply the distributive property.

$8 (x^{8} (- 7 {(5 - x)}^{6})) + 8 (8 {(5 - x)}^{7} x^{7})$

Step 4.1.5.2

Multiply $- 7$ by $8$ .

$- 56 (x^{8} ({(5 - x)}^{6})) + 8 (8 {(5 - x)}^{7} x^{7})$

Step 4.1.5.3

Multiply $8$ by $8$ .

$- 56 x^{8} {(5 - x)}^{6} + 64 ({(5 - x)}^{7} x^{7})$

Step 4.1.5.4

Factor $8 x^{7} {(5 - x)}^{6}$ out of $- 56 x^{8} {(5 - x)}^{6} + 64 {(5 - x)}^{7} x^{7}$ .

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Step 4.1.5.4.1

Factor $8 x^{7} {(5 - x)}^{6}$ out of $- 56 x^{8} {(5 - x)}^{6}$ .

$8 x^{7} {(5 - x)}^{6} (- 7 x) + 64 {(5 - x)}^{7} x^{7}$

Step 4.1.5.4.2

Factor $8 x^{7} {(5 - x)}^{6}$ out of $64 {(5 - x)}^{7} x^{7}$ .

$8 x^{7} {(5 - x)}^{6} (- 7 x) + 8 x^{7} {(5 - x)}^{6} (8 (5 - x))$

Step 4.1.5.4.3

Factor $8 x^{7} {(5 - x)}^{6}$ out of $8 x^{7} {(5 - x)}^{6} (- 7 x) + 8 x^{7} {(5 - x)}^{6} (8 (5 - x))$ .

$f' (x) = 8 x^{7} {(5 - x)}^{6} (- 7 x + 8 (5 - x))$

Step 4.2

The first derivative of $f (x)$ with respect to $x$ is $8 x^{7} {(5 - x)}^{6} (- 7 x + 8 (5 - x))$ .

$8 x^{7} {(5 - x)}^{6} (- 7 x + 8 (5 - x))$

Step 5

Set the first derivative equal to $0$ then solve the equation $8 x^{7} {(5 - x)}^{6} (- 7 x + 8 (5 - x)) = 0$ .

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Step 5.1

Set the first derivative equal to $0$ .

$8 x^{7} {(5 - x)}^{6} (- 7 x + 8 (5 - x)) = 0$

Step 5.2

If any individual factor on the left side of the equation is equal to $0$ , the entire expression will be equal to $0$ .

$x^{7} = 0$

${(5 - x)}^{6} = 0$

$- 7 x + 8 (5 - x) = 0$

Step 5.3

Set $x^{7}$ equal to $0$ and solve for $x$ .

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Step 5.3.1

Set $x^{7}$ equal to $0$ .

$x^{7} = 0$

Step 5.3.2

Solve $x^{7} = 0$ for $x$ .

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Step 5.3.2.1

Take the specified root of both sides of the equation to eliminate the exponent on the left side.

$x = \sqrt[7]{0}$

Step 5.3.2.2

Simplify $\sqrt[7]{0}$ .

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Step 5.3.2.2.1

Rewrite $0$ as $0^{7}$ .

$x = \sqrt[7]{0^{7}}$

Step 5.3.2.2.2

Pull terms out from under the radical, assuming real numbers.

$x = 0$

Step 5.4

Set ${(5 - x)}^{6}$ equal to $0$ and solve for $x$ .

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Step 5.4.1

Set ${(5 - x)}^{6}$ equal to $0$ .

${(5 - x)}^{6} = 0$

Step 5.4.2

Solve ${(5 - x)}^{6} = 0$ for $x$ .

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Step 5.4.2.1

Set the $5 - x$ equal to $0$ .

$5 - x = 0$

Step 5.4.2.2

Solve for $x$ .

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Step 5.4.2.2.1

Subtract $5$ from both sides of the equation.

$- x = - 5$

Step 5.4.2.2.2

Divide each term in $- x = - 5$ by $- 1$ and simplify.

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Step 5.4.2.2.2.1

Divide each term in $- x = - 5$ by $- 1$ .

$\frac{- x}{- 1} = \frac{- 5}{- 1}$

Step 5.4.2.2.2.2

Simplify the left side.

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Step 5.4.2.2.2.2.1

Dividing two negative values results in a positive value.

$\frac{x}{1} = \frac{- 5}{- 1}$

Step 5.4.2.2.2.2.2

Divide $x$ by $1$ .

$x = \frac{- 5}{- 1}$

Step 5.4.2.2.2.3

Simplify the right side.

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Step 5.4.2.2.2.3.1

Divide $- 5$ by $- 1$ .

$x = 5$

Step 5.5

Set $- 7 x + 8 (5 - x)$ equal to $0$ and solve for $x$ .

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Step 5.5.1

Set $- 7 x + 8 (5 - x)$ equal to $0$ .

$- 7 x + 8 (5 - x) = 0$

Step 5.5.2

Solve $- 7 x + 8 (5 - x) = 0$ for $x$ .

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Step 5.5.2.1

Simplify $- 7 x + 8 (5 - x)$ .

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Step 5.5.2.1.1

Simplify each term.

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Step 5.5.2.1.1.1

Apply the distributive property.

$- 7 x + 8 \cdot 5 + 8 (- x) = 0$

Step 5.5.2.1.1.2

Multiply $8$ by $5$ .

$- 7 x + 40 + 8 (- x) = 0$

Step 5.5.2.1.1.3

Multiply $- 1$ by $8$ .

$- 7 x + 40 - 8 x = 0$

Step 5.5.2.1.2

Subtract $8 x$ from $- 7 x$ .

$- 15 x + 40 = 0$

Step 5.5.2.2

Subtract $40$ from both sides of the equation.

$- 15 x = - 40$

Step 5.5.2.3

Divide each term in $- 15 x = - 40$ by $- 15$ and simplify.

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Step 5.5.2.3.1

Divide each term in $- 15 x = - 40$ by $- 15$ .

$\frac{- 15 x}{- 15} = \frac{- 40}{- 15}$

Step 5.5.2.3.2

Simplify the left side.

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Step 5.5.2.3.2.1

Cancel the common factor of $- 15$ .

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Step 5.5.2.3.2.1.1

Cancel the common factor.

$\frac{- 15 x}{- 15} = \frac{- 40}{- 15}$

Step 5.5.2.3.2.1.2

Divide $x$ by $1$ .

$x = \frac{- 40}{- 15}$

Step 5.5.2.3.3

Simplify the right side.

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Step 5.5.2.3.3.1

Cancel the common factor of $- 40$ and $- 15$ .

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Step 5.5.2.3.3.1.1

Factor $- 5$ out of $- 40$ .

$x = \frac{- 5 (8)}{- 15}$

Step 5.5.2.3.3.1.2

Cancel the common factors.

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Step 5.5.2.3.3.1.2.1

Factor $- 5$ out of $- 15$ .

$x = \frac{- 5 \cdot 8}{- 5 \cdot 3}$

Step 5.5.2.3.3.1.2.2

Cancel the common factor.

$x = \frac{- 5 \cdot 8}{- 5 \cdot 3}$

Step 5.5.2.3.3.1.2.3

Rewrite the expression.

$x = \frac{8}{3}$

Step 5.6

The final solution is all the values that make $8 x^{7} {(5 - x)}^{6} (- 7 x + 8 (5 - x)) = 0$ true.

$x = 0, 5, \frac{8}{3}$

Step 6

Find the values where the derivative is undefined.

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Step 6.1

The domain of the expression is all real numbers except where the expression is undefined. In this case, there is no real number that makes the expression undefined.

Step 7

Critical points to evaluate.

$x = 0, 5, \frac{8}{3}$

Step 8

Evaluate the second derivative at $x = 0$ . If the second derivative is positive, then this is a local minimum. If it is negative, then this is a local maximum.

$8 (- 15 {(0)}^{7} {(5 - (0))}^{6} + (- 15 \cdot 0 + 40) ({(0)}^{7} (- 6 {(5 - (0))}^{5}) + 7 {(5 - (0))}^{6} {(0)}^{6}))$

Step 9

Evaluate the second derivative.

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Step 9.1

Simplify each term.

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Step 9.1.1

Raising $0$ to any positive power yields $0$ .

$8 (- 15 \cdot 0 {(5 - (0))}^{6} + (- 15 \cdot 0 + 40) ({(0)}^{7} (- 6 {(5 - (0))}^{5}) + 7 {(5 - (0))}^{6} {(0)}^{6}))$

Step 9.1.2

Multiply $- 15$ by $0$ .

$8 (0 {(5 - (0))}^{6} + (- 15 \cdot 0 + 40) ({(0)}^{7} (- 6 {(5 - (0))}^{5}) + 7 {(5 - (0))}^{6} {(0)}^{6}))$

Step 9.1.3

Subtract $0$ from $5$ .

$8 (0 \cdot 5^{6} + (- 15 \cdot 0 + 40) ({(0)}^{7} (- 6 {(5 - (0))}^{5}) + 7 {(5 - (0))}^{6} {(0)}^{6}))$

Step 9.1.4

Raise $5$ to the power of $6$ .

$8 (0 \cdot 15625 + (- 15 \cdot 0 + 40) ({(0)}^{7} (- 6 {(5 - (0))}^{5}) + 7 {(5 - (0))}^{6} {(0)}^{6}))$

Step 9.1.5

Multiply $0$ by $15625$ .

$8 (0 + (- 15 \cdot 0 + 40) ({(0)}^{7} (- 6 {(5 - (0))}^{5}) + 7 {(5 - (0))}^{6} {(0)}^{6}))$

Step 9.1.6

Multiply $- 15$ by $0$ .

$8 (0 + (0 + 40) ({(0)}^{7} (- 6 {(5 - (0))}^{5}) + 7 {(5 - (0))}^{6} {(0)}^{6}))$

Step 9.1.7

Add $0$ and $40$ .

$8 (0 + 40 ({(0)}^{7} (- 6 {(5 - (0))}^{5}) + 7 {(5 - (0))}^{6} {(0)}^{6}))$

Step 9.1.8

Simplify each term.

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Step 9.1.8.1

Raising $0$ to any positive power yields $0$ .

$8 (0 + 40 (0 (- 6 {(5 - (0))}^{5}) + 7 {(5 - (0))}^{6} {(0)}^{6}))$

Step 9.1.8.2

Subtract $0$ from $5$ .

$8 (0 + 40 (0 (- 6 \cdot 5^{5}) + 7 {(5 - (0))}^{6} {(0)}^{6}))$

Step 9.1.8.3

Raise $5$ to the power of $5$ .

$8 (0 + 40 (0 (- 6 \cdot 3125) + 7 {(5 - (0))}^{6} {(0)}^{6}))$

Step 9.1.8.4

Multiply $0 (- 6 \cdot 3125)$ .

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Step 9.1.8.4.1

Multiply $- 6$ by $3125$ .

$8 (0 + 40 (0 \cdot - 18750 + 7 {(5 - (0))}^{6} {(0)}^{6}))$

Step 9.1.8.4.2

Multiply $0$ by $- 18750$ .

$8 (0 + 40 (0 + 7 {(5 - (0))}^{6} {(0)}^{6}))$

Step 9.1.8.5

Subtract $0$ from $5$ .

$8 (0 + 40 (0 + 7 \cdot 5^{6} {(0)}^{6}))$

Step 9.1.8.6

Raise $5$ to the power of $6$ .

$8 (0 + 40 (0 + 7 \cdot 15625 {(0)}^{6}))$

Step 9.1.8.7

Multiply $7$ by $15625$ .

$8 (0 + 40 (0 + 109375 {(0)}^{6}))$

Step 9.1.8.8

Raising $0$ to any positive power yields $0$ .

$8 (0 + 40 (0 + 109375 \cdot 0))$

Step 9.1.8.9

Multiply $109375$ by $0$ .

$8 (0 + 40 (0 + 0))$

Step 9.1.9

Add $0$ and $0$ .

$8 (0 + 40 \cdot 0)$

Step 9.1.10

Multiply $40$ by $0$ .

$8 (0 + 0)$

Step 9.2

Simplify the expression.

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Step 9.2.1

Add $0$ and $0$ .

$8 \cdot 0$

Step 9.2.2

Multiply $8$ by $0$ .

$0$

Step 10

Since there is at least one point with $0$ or undefined second derivative, apply the first derivative test.

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Step 10.1

Split $(- \infty, \infty)$ into separate intervals around the $x$ values that make the first derivative $0$ or undefined.

$(- \infty, 0) \cup (0, \frac{8}{3}) \cup (\frac{8}{3}, 5) \cup (5, \infty)$

Step 10.2

Substitute any number, such as $- 2$ , from the interval $(- \infty, 0)$ in the first derivative $8 x^{7} {(5 - x)}^{6} (- 7 x + 8 (5 - x))$ to check if the result is negative or positive.

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Step 10.2.1

Replace the variable $x$ with $- 2$ in the expression.

$f' (- 2) = 8 {(- 2)}^{7} {(5 - (- 2))}^{6} (- 7 \cdot - 2 + 8 (5 - (- 2)))$

Step 10.2.2

Simplify the result.

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Step 10.2.2.1

Simplify the expression.

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Step 10.2.2.1.1

Raise $- 2$ to the power of $7$ .

$f' (- 2) = 8 \cdot (- 128 {(5 - (- 2))}^{6} (- 7 \cdot - 2 + 8 (5 - (- 2))))$

Step 10.2.2.1.2

Multiply $8$ by $- 128$ .

$f' (- 2) = - 1024 {(5 - (- 2))}^{6} (- 7 \cdot - 2 + 8 (5 - (- 2)))$

Step 10.2.2.1.3

Multiply $- 1$ by $- 2$ .

$f' (- 2) = - 1024 {(5 + 2)}^{6} (- 7 \cdot - 2 + 8 (5 - (- 2)))$

Step 10.2.2.1.4

Add $5$ and $2$ .

$f' (- 2) = - 1024 \cdot (7^{6} (- 7 \cdot - 2 + 8 (5 - (- 2))))$

Step 10.2.2.1.5

Raise $7$ to the power of $6$ .

$f' (- 2) = - 1024 \cdot (117649 (- 7 \cdot - 2 + 8 (5 - (- 2))))$

Step 10.2.2.1.6

Multiply $- 1024$ by $117649$ .

$f' (- 2) = - 120472576 (- 7 \cdot - 2 + 8 (5 - (- 2)))$

Step 10.2.2.2

Simplify each term.

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Step 10.2.2.2.1

Multiply $- 7$ by $- 2$ .

$f' (- 2) = - 120472576 (14 + 8 (5 - (- 2)))$

Step 10.2.2.2.2

Multiply $- 1$ by $- 2$ .

$f' (- 2) = - 120472576 (14 + 8 (5 + 2))$

Step 10.2.2.2.3

Add $5$ and $2$ .

$f' (- 2) = - 120472576 (14 + 8 \cdot 7)$

Step 10.2.2.2.4

Multiply $8$ by $7$ .

$f' (- 2) = - 120472576 (14 + 56)$

Step 10.2.2.3

Simplify the expression.

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Step 10.2.2.3.1

Add $14$ and $56$ .

$f' (- 2) = - 120472576 \cdot 70$

Step 10.2.2.3.2

Multiply $- 120472576$ by $70$ .

$f' (- 2) = - 8433080320$

Step 10.2.2.4

The final answer is $- 8433080320$ .

$- 8433080320$

Step 10.3

Substitute any number, such as $1$ , from the interval $(0, \frac{8}{3})$ in the first derivative $8 x^{7} {(5 - x)}^{6} (- 7 x + 8 (5 - x))$ to check if the result is negative or positive.

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Step 10.3.1

Replace the variable $x$ with $1$ in the expression.

$f' (1) = 8 {(1)}^{7} {(5 - (1))}^{6} (- 7 \cdot 1 + 8 (5 - (1)))$

Step 10.3.2

Simplify the result.

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Step 10.3.2.1

Simplify the expression.

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Step 10.3.2.1.1

One to any power is one.

$f' (1) = 8 \cdot (1 {(5 - (1))}^{6} (- 7 \cdot 1 + 8 (5 - (1))))$

Step 10.3.2.1.2

Multiply $8$ by $1$ .

$f' (1) = 8 {(5 - (1))}^{6} (- 7 \cdot 1 + 8 (5 - (1)))$

Step 10.3.2.1.3

Multiply $- 1$ by $1$ .

$f' (1) = 8 {(5 - 1)}^{6} (- 7 \cdot 1 + 8 (5 - (1)))$

Step 10.3.2.1.4

Subtract $1$ from $5$ .

$f' (1) = 8 \cdot (4^{6} (- 7 \cdot 1 + 8 (5 - (1))))$

Step 10.3.2.1.5

Raise $4$ to the power of $6$ .

$f' (1) = 8 \cdot (4096 (- 7 \cdot 1 + 8 (5 - (1))))$

Step 10.3.2.1.6

Multiply $8$ by $4096$ .

$f' (1) = 32768 (- 7 \cdot 1 + 8 (5 - (1)))$

Step 10.3.2.2

Simplify each term.

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Step 10.3.2.2.1

Multiply $- 7$ by $1$ .

$f' (1) = 32768 (- 7 + 8 (5 - (1)))$

Step 10.3.2.2.2

Multiply $- 1$ by $1$ .

$f' (1) = 32768 (- 7 + 8 (5 - 1))$

Step 10.3.2.2.3

Subtract $1$ from $5$ .

$f' (1) = 32768 (- 7 + 8 \cdot 4)$

Step 10.3.2.2.4

Multiply $8$ by $4$ .

$f' (1) = 32768 (- 7 + 32)$

Step 10.3.2.3

Simplify the expression.

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Step 10.3.2.3.1

Add $- 7$ and $32$ .

$f' (1) = 32768 \cdot 25$

Step 10.3.2.3.2

Multiply $32768$ by $25$ .

$f' (1) = 819200$

Step 10.3.2.4

The final answer is $819200$ .

$819200$

Step 10.4

Substitute any number, such as $4$ , from the interval $(\frac{8}{3}, 5)$ in the first derivative $8 x^{7} {(5 - x)}^{6} (- 7 x + 8 (5 - x))$ to check if the result is negative or positive.

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Step 10.4.1

Replace the variable $x$ with $4$ in the expression.

$f' (4) = 8 {(4)}^{7} {(5 - (4))}^{6} (- 7 \cdot 4 + 8 (5 - (4)))$

Step 10.4.2

Simplify the result.

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Step 10.4.2.1

Simplify the expression.

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Step 10.4.2.1.1

Raise $4$ to the power of $7$ .

$f' (4) = 8 \cdot (16384 {(5 - (4))}^{6} (- 7 \cdot 4 + 8 (5 - (4))))$

Step 10.4.2.1.2

Multiply $8$ by $16384$ .

$f' (4) = 131072 {(5 - (4))}^{6} (- 7 \cdot 4 + 8 (5 - (4)))$

Step 10.4.2.1.3

Multiply $- 1$ by $4$ .

$f' (4) = 131072 {(5 - 4)}^{6} (- 7 \cdot 4 + 8 (5 - (4)))$

Step 10.4.2.1.4

Subtract $4$ from $5$ .

$f' (4) = 131072 \cdot (1^{6} (- 7 \cdot 4 + 8 (5 - (4))))$

Step 10.4.2.1.5

One to any power is one.

$f' (4) = 131072 \cdot (1 (- 7 \cdot 4 + 8 (5 - (4))))$

Step 10.4.2.1.6

Multiply $131072$ by $1$ .

$f' (4) = 131072 (- 7 \cdot 4 + 8 (5 - (4)))$

Step 10.4.2.2

Simplify each term.

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Step 10.4.2.2.1

Multiply $- 7$ by $4$ .

$f' (4) = 131072 (- 28 + 8 (5 - (4)))$

Step 10.4.2.2.2

Multiply $- 1$ by $4$ .

$f' (4) = 131072 (- 28 + 8 (5 - 4))$

Step 10.4.2.2.3

Subtract $4$ from $5$ .

$f' (4) = 131072 (- 28 + 8 \cdot 1)$

Step 10.4.2.2.4

Multiply $8$ by $1$ .

$f' (4) = 131072 (- 28 + 8)$

Step 10.4.2.3

Simplify the expression.

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Step 10.4.2.3.1

Add $- 28$ and $8$ .

$f' (4) = 131072 \cdot - 20$

Step 10.4.2.3.2

Multiply $131072$ by $- 20$ .

$f' (4) = - 2621440$

Step 10.4.2.4

The final answer is $- 2621440$ .

$- 2621440$

Step 10.5

Substitute any number, such as $8$ , from the interval $(5, \infty)$ in the first derivative $8 x^{7} {(5 - x)}^{6} (- 7 x + 8 (5 - x))$ to check if the result is negative or positive.

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Step 10.5.1

Replace the variable $x$ with $8$ in the expression.

$f' (8) = 8 {(8)}^{7} {(5 - (8))}^{6} (- 7 \cdot 8 + 8 (5 - (8)))$

Step 10.5.2

Simplify the result.

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Step 10.5.2.1

Multiply $8$ by ${(8)}^{7}$ by adding the exponents.

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Step 10.5.2.1.1

Multiply $8$ by ${(8)}^{7}$ .

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Step 10.5.2.1.1.1

Raise $8$ to the power of $1$ .

$f' (8) = 8 {(8)}^{7} {(5 - (8))}^{6} (- 7 \cdot 8 + 8 (5 - (8)))$

Step 10.5.2.1.1.2

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$f' (8) = 8^{1 + 7} {(5 - (8))}^{6} (- 7 \cdot 8 + 8 (5 - (8)))$

Step 10.5.2.1.2

Add $1$ and $7$ .

$f' (8) = 8^{8} {(5 - (8))}^{6} (- 7 \cdot 8 + 8 (5 - (8)))$

Step 10.5.2.2

Simplify the expression.

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Step 10.5.2.2.1

Raise $8$ to the power of $8$ .

$f' (8) = 16777216 {(5 - (8))}^{6} (- 7 \cdot 8 + 8 (5 - (8)))$

Step 10.5.2.2.2

Multiply $- 1$ by $8$ .

$f' (8) = 16777216 {(5 - 8)}^{6} (- 7 \cdot 8 + 8 (5 - (8)))$

Step 10.5.2.2.3

Subtract $8$ from $5$ .

$f' (8) = 16777216 {(- 3)}^{6} (- 7 \cdot 8 + 8 (5 - (8)))$

Step 10.5.2.2.4

Raise $- 3$ to the power of $6$ .

$f' (8) = 16777216 \cdot (729 (- 7 \cdot 8 + 8 (5 - (8))))$

Step 10.5.2.2.5

Multiply $16777216$ by $729$ .

$f' (8) = 12230590464 (- 7 \cdot 8 + 8 (5 - (8)))$

Step 10.5.2.3

Simplify each term.

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Step 10.5.2.3.1

Multiply $- 7$ by $8$ .

$f' (8) = 12230590464 (- 56 + 8 (5 - (8)))$

Step 10.5.2.3.2

Multiply $- 1$ by $8$ .

$f' (8) = 12230590464 (- 56 + 8 (5 - 8))$

Step 10.5.2.3.3

Subtract $8$ from $5$ .

$f' (8) = 12230590464 (- 56 + 8 \cdot - 3)$

Step 10.5.2.3.4

Multiply $8$ by $- 3$ .

$f' (8) = 12230590464 (- 56 - 24)$

Step 10.5.2.4

Simplify the expression.

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Step 10.5.2.4.1

Subtract $24$ from $- 56$ .

$f' (8) = 12230590464 \cdot - 80$

Step 10.5.2.4.2

Multiply $12230590464$ by $- 80$ .

$f' (8) = - 978447237120$

Step 10.5.2.5

The final answer is $- 978447237120$ .

$- 978447237120$

Step 10.6

Since the first derivative changed signs from negative to positive around $x = 0$ , then $x = 0$ is a local minimum.

$x = 0$ is a local minimum

Step 10.7

Since the first derivative changed signs from positive to negative around $x = \frac{8}{3}$ , then $x = \frac{8}{3}$ is a local maximum.

$x = \frac{8}{3}$ is a local maximum

Step 10.8

Since the first derivative did not change signs around $x = 5$ , this is not a local maximum or minimum.

Not a local maximum or minimum

Step 10.9

These are the local extrema for $f (x) = 8 x^{8} {(5 - x)}^{7}$ .

$x = 0$ is a local minimum

$x = \frac{8}{3}$ is a local maximum

$x = 0$ is a local minimum

$x = \frac{8}{3}$ is a local maximum

Step 11