Calculus Examples

$f (x) = (8 - x) {(x + 1)}^{2}$

Step 1

Find the first derivative.

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Step 1.1

Find the first derivative.

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Step 1.1.1

Rewrite ${(x + 1)}^{2}$ as $(x + 1) (x + 1)$ .

$\frac{d}{d x} [(8 - x) ((x + 1) (x + 1))]$

Step 1.1.2

Expand $(x + 1) (x + 1)$ using the FOIL Method.

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Step 1.1.2.1

Apply the distributive property.

$\frac{d}{d x} [(8 - x) (x (x + 1) + 1 (x + 1))]$

Step 1.1.2.2

Apply the distributive property.

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

Step 1.1.2.3

Apply the distributive property.

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

Step 1.1.3

Simplify and combine like terms.

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Step 1.1.3.1

Simplify each term.

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Step 1.1.3.1.1

Multiply $x$ by $x$ .

$\frac{d}{d x} [(8 - x) (x^{2} + x \cdot 1 + 1 x + 1 \cdot 1)]$

Step 1.1.3.1.2

Multiply $x$ by $1$ .

$\frac{d}{d x} [(8 - x) (x^{2} + x + 1 x + 1 \cdot 1)]$

Step 1.1.3.1.3

Multiply $x$ by $1$ .

$\frac{d}{d x} [(8 - x) (x^{2} + x + x + 1 \cdot 1)]$

Step 1.1.3.1.4

Multiply $1$ by $1$ .

$\frac{d}{d x} [(8 - x) (x^{2} + x + x + 1)]$

Step 1.1.3.2

Add $x$ and $x$ .

$\frac{d}{d x} [(8 - x) (x^{2} + 2 x + 1)]$

Step 1.1.4

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 $f (x) = 8 - x$ and $g (x) = x^{2} + 2 x + 1$ .

$(8 - x) \frac{d}{d x} [x^{2} + 2 x + 1] + (x^{2} + 2 x + 1) \frac{d}{d x} [8 - x]$

Step 1.1.5

Differentiate.

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Step 1.1.5.1

By the Sum Rule, the derivative of $x^{2} + 2 x + 1$ with respect to $x$ is $\frac{d}{d x} [x^{2}] + \frac{d}{d x} [2 x] + \frac{d}{d x} [1]$ .

$(8 - x) (\frac{d}{d x} [x^{2}] + \frac{d}{d x} [2 x] + \frac{d}{d x} [1]) + (x^{2} + 2 x + 1) \frac{d}{d x} [8 - x]$

Step 1.1.5.2

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 2$ .

$(8 - x) (2 x + \frac{d}{d x} [2 x] + \frac{d}{d x} [1]) + (x^{2} + 2 x + 1) \frac{d}{d x} [8 - x]$

Step 1.1.5.3

Since $2$ is constant with respect to $x$ , the derivative of $2 x$ with respect to $x$ is $2 \frac{d}{d x} [x]$ .

$(8 - x) (2 x + 2 \frac{d}{d x} [x] + \frac{d}{d x} [1]) + (x^{2} + 2 x + 1) \frac{d}{d x} [8 - x]$

Step 1.1.5.4

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

$(8 - x) (2 x + 2 \cdot 1 + \frac{d}{d x} [1]) + (x^{2} + 2 x + 1) \frac{d}{d x} [8 - x]$

Step 1.1.5.5

Multiply $2$ by $1$ .

$(8 - x) (2 x + 2 + \frac{d}{d x} [1]) + (x^{2} + 2 x + 1) \frac{d}{d x} [8 - x]$

Step 1.1.5.6

Since $1$ is constant with respect to $x$ , the derivative of $1$ with respect to $x$ is $0$ .

$(8 - x) (2 x + 2 + 0) + (x^{2} + 2 x + 1) \frac{d}{d x} [8 - x]$

Step 1.1.5.7

Add $2 x + 2$ and $0$ .

$(8 - x) (2 x + 2) + (x^{2} + 2 x + 1) \frac{d}{d x} [8 - x]$

Step 1.1.5.8

By the Sum Rule, the derivative of $8 - x$ with respect to $x$ is $\frac{d}{d x} [8] + \frac{d}{d x} [- x]$ .

$(8 - x) (2 x + 2) + (x^{2} + 2 x + 1) (\frac{d}{d x} [8] + \frac{d}{d x} [- x])$

Step 1.1.5.9

Since $8$ is constant with respect to $x$ , the derivative of $8$ with respect to $x$ is $0$ .

$(8 - x) (2 x + 2) + (x^{2} + 2 x + 1) (0 + \frac{d}{d x} [- x])$

Step 1.1.5.10

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

$(8 - x) (2 x + 2) + (x^{2} + 2 x + 1) \frac{d}{d x} [- x]$

Step 1.1.5.11

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

$(8 - x) (2 x + 2) + (x^{2} + 2 x + 1) (- \frac{d}{d x} [x])$

Step 1.1.5.12

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

$(8 - x) (2 x + 2) + (x^{2} + 2 x + 1) (- 1 \cdot 1)$

Step 1.1.5.13

Simplify the expression.

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Step 1.1.5.13.1

Multiply $- 1$ by $1$ .

$(8 - x) (2 x + 2) + (x^{2} + 2 x + 1) \cdot - 1$

Step 1.1.5.13.2

Move $- 1$ to the left of $x^{2} + 2 x + 1$ .

$(8 - x) (2 x + 2) - 1 \cdot (x^{2} + 2 x + 1)$

Step 1.1.5.13.3

Rewrite $- 1 (x^{2} + 2 x + 1)$ as $- (x^{2} + 2 x + 1)$ .

$(8 - x) (2 x + 2) - (x^{2} + 2 x + 1)$

Step 1.1.6

Simplify.

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Step 1.1.6.1

Apply the distributive property.

$(8 - x) (2 x + 2) - x^{2} - (2 x) - 1 \cdot 1$

Step 1.1.6.2

Apply the distributive property.

$(8 - x) (2 x) + (8 - x) \cdot 2 - x^{2} - (2 x) - 1 \cdot 1$

Step 1.1.6.3

Apply the distributive property.

$8 (2 x) - x (2 x) + (8 - x) \cdot 2 - x^{2} - (2 x) - 1 \cdot 1$

Step 1.1.6.4

Apply the distributive property.

$8 (2 x) - x (2 x) + 8 \cdot 2 - x \cdot 2 - x^{2} - (2 x) - 1 \cdot 1$

Step 1.1.6.5

Combine terms.

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Step 1.1.6.5.1

Multiply $2$ by $8$ .

$16 x - x (2 x) + 8 \cdot 2 - x \cdot 2 - x^{2} - (2 x) - 1 \cdot 1$

Step 1.1.6.5.2

Multiply $2$ by $- 1$ .

$16 x - 2 x \cdot x + 8 \cdot 2 - x \cdot 2 - x^{2} - (2 x) - 1 \cdot 1$

Step 1.1.6.5.3

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

$16 x - 2 (x^{1} x) + 8 \cdot 2 - x \cdot 2 - x^{2} - (2 x) - 1 \cdot 1$

Step 1.1.6.5.4

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

$16 x - 2 (x^{1} x^{1}) + 8 \cdot 2 - x \cdot 2 - x^{2} - (2 x) - 1 \cdot 1$

Step 1.1.6.5.5

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

$16 x - 2 x^{1 + 1} + 8 \cdot 2 - x \cdot 2 - x^{2} - (2 x) - 1 \cdot 1$

Step 1.1.6.5.6

Add $1$ and $1$ .

$16 x - 2 x^{2} + 8 \cdot 2 - x \cdot 2 - x^{2} - (2 x) - 1 \cdot 1$

Step 1.1.6.5.7

Multiply $8$ by $2$ .

$16 x - 2 x^{2} + 16 - x \cdot 2 - x^{2} - (2 x) - 1 \cdot 1$

Step 1.1.6.5.8

Multiply $2$ by $- 1$ .

$16 x - 2 x^{2} + 16 - 2 x - x^{2} - (2 x) - 1 \cdot 1$

Step 1.1.6.5.9

Subtract $2 x$ from $16 x$ .

$14 x - 2 x^{2} + 16 - x^{2} - (2 x) - 1 \cdot 1$

Step 1.1.6.5.10

Multiply $2$ by $- 1$ .

$14 x - 2 x^{2} + 16 - x^{2} - 2 x - 1 \cdot 1$

Step 1.1.6.5.11

Multiply $- 1$ by $1$ .

$14 x - 2 x^{2} + 16 - x^{2} - 2 x - 1$

Step 1.1.6.5.12

Subtract $x^{2}$ from $- 2 x^{2}$ .

$14 x - 3 x^{2} + 16 - 2 x - 1$

Step 1.1.6.5.13

Subtract $2 x$ from $14 x$ .

$12 x - 3 x^{2} + 16 - 1$

Step 1.1.6.5.14

Subtract $1$ from $16$ .

$12 x - 3 x^{2} + 15$

Step 1.1.6.6

Reorder terms.

$f' (x) = - 3 x^{2} + 12 x + 15$

Step 1.2

The first derivative of $f (x)$ with respect to $x$ is $- 3 x^{2} + 12 x + 15$ .

$- 3 x^{2} + 12 x + 15$

Step 2

Set the first derivative equal to $0$ then solve the equation $- 3 x^{2} + 12 x + 15 = 0$ .

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Step 2.1

Set the first derivative equal to $0$ .

$- 3 x^{2} + 12 x + 15 = 0$

Step 2.2

Factor the left side of the equation.

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Step 2.2.1

Factor $- 3$ out of $- 3 x^{2} + 12 x + 15$ .

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Step 2.2.1.1

Factor $- 3$ out of $- 3 x^{2}$ .

$- 3 x^{2} + 12 x + 15 = 0$

Step 2.2.1.2

Factor $- 3$ out of $12 x$ .

$- 3 x^{2} - 3 (- 4 x) + 15 = 0$

Step 2.2.1.3

Factor $- 3$ out of $15$ .

$- 3 x^{2} - 3 (- 4 x) - 3 \cdot - 5 = 0$

Step 2.2.1.4

Factor $- 3$ out of $- 3 (x^{2}) - 3 (- 4 x)$ .

$- 3 (x^{2} - 4 x) - 3 \cdot - 5 = 0$

Step 2.2.1.5

Factor $- 3$ out of $- 3 (x^{2} - 4 x) - 3 (- 5)$ .

$- 3 (x^{2} - 4 x - 5) = 0$

Step 2.2.2

Factor.

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Step 2.2.2.1

Factor $x^{2} - 4 x - 5$ using the AC method.

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Step 2.2.2.1.1

Consider the form $x^{2} + b x + c$ . Find a pair of integers whose product is $c$ and whose sum is $b$ . In this case, whose product is $- 5$ and whose sum is $- 4$ .

$- 5, 1$

Step 2.2.2.1.2

Write the factored form using these integers.

$- 3 ((x - 5) (x + 1)) = 0$

Step 2.2.2.2

Remove unnecessary parentheses.

$- 3 (x - 5) (x + 1) = 0$

Step 2.3

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

$x - 5 = 0$

$x + 1 = 0$

Step 2.4

Set $x - 5$ equal to $0$ and solve for $x$ .

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Step 2.4.1

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

$x - 5 = 0$

Step 2.4.2

Add $5$ to both sides of the equation.

$x = 5$

Step 2.5

Set $x + 1$ equal to $0$ and solve for $x$ .

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Step 2.5.1

Set $x + 1$ equal to $0$ .

$x + 1 = 0$

Step 2.5.2

Subtract $1$ from both sides of the equation.

$x = - 1$

Step 2.6

The final solution is all the values that make $- 3 (x - 5) (x + 1) = 0$ true.

$x = 5, - 1$

Step 3

Find the values where the derivative is undefined.

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Step 3.1

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 4

Evaluate $(8 - x) {(x + 1)}^{2}$ at each $x$ value where the derivative is $0$ or undefined.

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Step 4.1

Evaluate at $x = 5$ .

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Step 4.1.1

Substitute $5$ for $x$ .

$(8 - (5)) {((5) + 1)}^{2}$

Step 4.1.2

Simplify.

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Step 4.1.2.1

Multiply $- 1$ by $5$ .

$(8 - 5) {((5) + 1)}^{2}$

Step 4.1.2.2

Subtract $5$ from $8$ .

$3 {((5) + 1)}^{2}$

Step 4.1.2.3

Add $5$ and $1$ .

$3 \cdot 6^{2}$

Step 4.1.2.4

Raise $6$ to the power of $2$ .

$3 \cdot 36$

Step 4.1.2.5

Multiply $3$ by $36$ .

$108$

Step 4.2

Evaluate at $x = - 1$ .

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Step 4.2.1

Substitute $- 1$ for $x$ .

$(8 - (- 1)) {((- 1) + 1)}^{2}$

Step 4.2.2

Simplify.

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Step 4.2.2.1

Multiply $- 1$ by $- 1$ .

$(8 + 1) {((- 1) + 1)}^{2}$

Step 4.2.2.2

Add $8$ and $1$ .

$9 {((- 1) + 1)}^{2}$

Step 4.2.2.3

Add $- 1$ and $1$ .

$9 \cdot 0^{2}$

Step 4.2.2.4

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

$9 \cdot 0$

Step 4.2.2.5

Multiply $9$ by $0$ .

$0$

Step 4.3

List all of the points.

$(5, 108), (- 1, 0)$

Step 5