Calculus Examples

$f (x) = 7 - 4 x - 4 x^{2}$

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

Differentiate.

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Step 1.1.1.1

By the Sum Rule, the derivative of $7 - 4 x - 4 x^{2}$ with respect to $x$ is $\frac{d}{d x} [7] + \frac{d}{d x} [- 4 x] + \frac{d}{d x} [- 4 x^{2}]$ .

$\frac{d}{d x} [7] + \frac{d}{d x} [- 4 x] + \frac{d}{d x} [- 4 x^{2}]$

Step 1.1.1.2

Since $7$ is constant with respect to $x$ , the derivative of $7$ with respect to $x$ is $0$ .

$0 + \frac{d}{d x} [- 4 x] + \frac{d}{d x} [- 4 x^{2}]$

Step 1.1.2

Evaluate $\frac{d}{d x} [- 4 x]$ .

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Step 1.1.2.1

Since $- 4$ is constant with respect to $x$ , the derivative of $- 4 x$ with respect to $x$ is $- 4 \frac{d}{d x} [x]$ .

$0 - 4 \frac{d}{d x} [x] + \frac{d}{d x} [- 4 x^{2}]$

Step 1.1.2.2

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

$0 - 4 \cdot 1 + \frac{d}{d x} [- 4 x^{2}]$

Step 1.1.2.3

Multiply $- 4$ by $1$ .

$0 - 4 + \frac{d}{d x} [- 4 x^{2}]$

Step 1.1.3

Evaluate $\frac{d}{d x} [- 4 x^{2}]$ .

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Step 1.1.3.1

Since $- 4$ is constant with respect to $x$ , the derivative of $- 4 x^{2}$ with respect to $x$ is $- 4 \frac{d}{d x} [x^{2}]$ .

$0 - 4 - 4 \frac{d}{d x} [x^{2}]$

Step 1.1.3.2

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

$0 - 4 - 4 (2 x)$

Step 1.1.3.3

Multiply $2$ by $- 4$ .

$0 - 4 - 8 x$

Step 1.1.4

Simplify.

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Step 1.1.4.1

Subtract $4$ from $0$ .

$- 4 - 8 x$

Step 1.1.4.2

Reorder terms.

$f' (x) = - 8 x - 4$

Step 1.2

The first derivative of $f (x)$ with respect to $x$ is $- 8 x - 4$ .

$- 8 x - 4$

Step 2

Set the first derivative equal to $0$ then solve the equation $- 8 x - 4 = 0$ .

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Step 2.1

Set the first derivative equal to $0$ .

$- 8 x - 4 = 0$

Step 2.2

Add $4$ to both sides of the equation.

$- 8 x = 4$

Step 2.3

Divide each term in $- 8 x = 4$ by $- 8$ and simplify.

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Step 2.3.1

Divide each term in $- 8 x = 4$ by $- 8$ .

$\frac{- 8 x}{- 8} = \frac{4}{- 8}$

Step 2.3.2

Simplify the left side.

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Step 2.3.2.1

Cancel the common factor of $- 8$ .

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Step 2.3.2.1.1

Cancel the common factor.

$\frac{- 8 x}{- 8} = \frac{4}{- 8}$

Step 2.3.2.1.2

Divide $x$ by $1$ .

$x = \frac{4}{- 8}$

Step 2.3.3

Simplify the right side.

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Step 2.3.3.1

Cancel the common factor of $4$ and $- 8$ .

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Step 2.3.3.1.1

Factor $4$ out of $4$ .

$x = \frac{4 (1)}{- 8}$

Step 2.3.3.1.2

Cancel the common factors.

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Step 2.3.3.1.2.1

Factor $4$ out of $- 8$ .

$x = \frac{4 \cdot 1}{4 \cdot - 2}$

Step 2.3.3.1.2.2

Cancel the common factor.

$x = \frac{4 \cdot 1}{4 \cdot - 2}$

Step 2.3.3.1.2.3

Rewrite the expression.

$x = \frac{1}{- 2}$

Step 2.3.3.2

Move the negative in front of the fraction.

$x = - \frac{1}{2}$

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 $7 - 4 x - 4 x^{2}$ at each $x$ value where the derivative is $0$ or undefined.

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Step 4.1

Evaluate at $x = - \frac{1}{2}$ .

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Step 4.1.1

Substitute $- \frac{1}{2}$ for $x$ .

$7 - 4 (- \frac{1}{2}) - 4 {(- \frac{1}{2})}^{2}$

Step 4.1.2

Simplify.

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Step 4.1.2.1

Simplify each term.

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Step 4.1.2.1.1

Cancel the common factor of $2$ .

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Step 4.1.2.1.1.1

Move the leading negative in $- \frac{1}{2}$ into the numerator.

$7 - 4 (\frac{- 1}{2}) - 4 {(- \frac{1}{2})}^{2}$

Step 4.1.2.1.1.2

Factor $2$ out of $- 4$ .

$7 + 2 (- 2) \frac{- 1}{2} - 4 {(- \frac{1}{2})}^{2}$

Step 4.1.2.1.1.3

Cancel the common factor.

$7 + 2 \cdot - 2 \frac{- 1}{2} - 4 {(- \frac{1}{2})}^{2}$

Step 4.1.2.1.1.4

Rewrite the expression.

$7 - 2 \cdot - 1 - 4 {(- \frac{1}{2})}^{2}$

Step 4.1.2.1.2

Multiply $- 2$ by $- 1$ .

$7 + 2 - 4 {(- \frac{1}{2})}^{2}$

Step 4.1.2.1.3

Use the power rule ${(a b)}^{n} = a^{n} b^{n}$ to distribute the exponent.

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Step 4.1.2.1.3.1

Apply the product rule to $- \frac{1}{2}$ .

$7 + 2 - 4 ({(- 1)}^{2} {(\frac{1}{2})}^{2})$

Step 4.1.2.1.3.2

Apply the product rule to $\frac{1}{2}$ .

$7 + 2 - 4 ({(- 1)}^{2} \frac{1^{2}}{2^{2}})$

Step 4.1.2.1.4

Raise $- 1$ to the power of $2$ .

$7 + 2 - 4 (1 \frac{1^{2}}{2^{2}})$

Step 4.1.2.1.5

Multiply $\frac{1^{2}}{2^{2}}$ by $1$ .

$7 + 2 - 4 \frac{1^{2}}{2^{2}}$

Step 4.1.2.1.6

One to any power is one.

$7 + 2 - 4 \frac{1}{2^{2}}$

Step 4.1.2.1.7

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

$7 + 2 - 4 (\frac{1}{4})$

Step 4.1.2.1.8

Cancel the common factor of $4$ .

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Step 4.1.2.1.8.1

Factor $4$ out of $- 4$ .

$7 + 2 + 4 (- 1) \frac{1}{4}$

Step 4.1.2.1.8.2

Cancel the common factor.

$7 + 2 + 4 \cdot - 1 \frac{1}{4}$

Step 4.1.2.1.8.3

Rewrite the expression.

$7 + 2 - 1$

Step 4.1.2.2

Simplify by adding and subtracting.

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Step 4.1.2.2.1

Add $7$ and $2$ .

$9 - 1$

Step 4.1.2.2.2

Subtract $1$ from $9$ .

$8$

Step 4.2

List all of the points.

$(- \frac{1}{2}, 8)$

Step 5