Calculus Examples

$f (x) = x^{2} + x - 4$ , $[0, 8]$

Step 1

Find the critical points.

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Step 1.1

Find the first derivative.

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Step 1.1.1

Find the first derivative.

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Step 1.1.1.1

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

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

Step 1.1.1.2

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

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

Step 1.1.1.3

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

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

Step 1.1.1.4

Since $- 4$ is constant with respect to $x$ , the derivative of $- 4$ with respect to $x$ is $0$ .

$2 x + 1 + 0$

Step 1.1.1.5

Add $2 x + 1$ and $0$ .

$f' (x) = 2 x + 1$

Step 1.1.2

The first derivative of $f (x)$ with respect to $x$ is $2 x + 1$ .

$2 x + 1$

Step 1.2

Set the first derivative equal to $0$ then solve the equation $2 x + 1 = 0$ .

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Step 1.2.1

Set the first derivative equal to $0$ .

$2 x + 1 = 0$

Step 1.2.2

Subtract $1$ from both sides of the equation.

$2 x = - 1$

Step 1.2.3

Divide each term in $2 x = - 1$ by $2$ and simplify.

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Step 1.2.3.1

Divide each term in $2 x = - 1$ by $2$ .

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

Step 1.2.3.2

Simplify the left side.

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Step 1.2.3.2.1

Cancel the common factor of $2$ .

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Step 1.2.3.2.1.1

Cancel the common factor.

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

Step 1.2.3.2.1.2

Divide $x$ by $1$ .

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

Step 1.2.3.3

Simplify the right side.

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Step 1.2.3.3.1

Move the negative in front of the fraction.

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

Step 1.3

Find the values where the derivative is undefined.

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Step 1.3.1

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 1.4

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

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Step 1.4.1

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

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Step 1.4.1.1

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

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

Step 1.4.1.2

Simplify.

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Step 1.4.1.2.1

Remove parentheses.

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

Step 1.4.1.2.2

Simplify each term.

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Step 1.4.1.2.2.1

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

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Step 1.4.1.2.2.1.1

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

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

Step 1.4.1.2.2.1.2

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

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

Step 1.4.1.2.2.2

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

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

Step 1.4.1.2.2.3

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

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

Step 1.4.1.2.2.4

One to any power is one.

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

Step 1.4.1.2.2.5

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

$\frac{1}{4} - \frac{1}{2} - 4$

Step 1.4.1.2.3

Find the common denominator.

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Step 1.4.1.2.3.1

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

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

Step 1.4.1.2.3.2

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

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

Step 1.4.1.2.3.3

Write $- 4$ as a fraction with denominator $1$ .

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

Step 1.4.1.2.3.4

Multiply $\frac{- 4}{1}$ by $\frac{4}{4}$ .

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

Step 1.4.1.2.3.5

Multiply $\frac{- 4}{1}$ by $\frac{4}{4}$ .

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

Step 1.4.1.2.3.6

Multiply $2$ by $2$ .

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

Step 1.4.1.2.4

Combine the numerators over the common denominator.

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

Step 1.4.1.2.5

Simplify the expression.

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Step 1.4.1.2.5.1

Multiply $- 4$ by $4$ .

$\frac{1 - 2 - 16}{4}$

Step 1.4.1.2.5.2

Subtract $2$ from $1$ .

$\frac{- 1 - 16}{4}$

Step 1.4.1.2.5.3

Subtract $16$ from $- 1$ .

$\frac{- 17}{4}$

Step 1.4.1.2.5.4

Move the negative in front of the fraction.

$- \frac{17}{4}$

Step 1.4.2

List all of the points.

$(- \frac{1}{2}, - \frac{17}{4})$

Step 2

Exclude the points that are not on the interval.

Step 3

Evaluate at the included endpoints.

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Step 3.1

Evaluate at $x = 0$ .

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Step 3.1.1

Substitute $0$ for $x$ .

${(0)}^{2} + 0 - 4$

Step 3.1.2

Simplify.

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Step 3.1.2.1

Remove parentheses.

${(0)}^{2} + 0 - 4$

Step 3.1.2.2

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

$0 + 0 - 4$

Step 3.1.2.3

Add $0$ and $0$ .

$0 - 4$

Step 3.1.2.4

Subtract $4$ from $0$ .

$- 4$

Step 3.2

Evaluate at $x = 8$ .

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Step 3.2.1

Substitute $8$ for $x$ .

${(8)}^{2} + 8 - 4$

Step 3.2.2

Simplify.

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Step 3.2.2.1

Remove parentheses.

${(8)}^{2} + 8 - 4$

Step 3.2.2.2

Raise $8$ to the power of $2$ .

$64 + 8 - 4$

Step 3.2.2.3

Add $64$ and $8$ .

$72 - 4$

Step 3.2.2.4

Subtract $4$ from $72$ .

$68$

Step 3.3

List all of the points.

$(0, - 4), (8, 68)$

Step 4

Compare the $f (x)$ values found for each value of $x$ in order to determine the absolute maximum and minimum over the given interval. The maximum will occur at the highest $f (x)$ value and the minimum will occur at the lowest $f (x)$ value.

Absolute Maximum: $(8, 68)$

Absolute Minimum: $(0, - 4)$

Step 5