Calculus Examples

f (x) = \frac{7}{x}

$f (x) = \frac{7}{x}$ ,

x \geq 7

$x \geq 7$

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

Since

7

$7$ is constant with respect to

x

$x$ , the derivative of

\frac{7}{x}

$\frac{7}{x}$ with respect to

x

$x$ is

7 \frac{d}{d x} [\frac{1}{x}]

$7 \frac{d}{d x} [\frac{1}{x}]$ .

7 \frac{d}{d x} [\frac{1}{x}]

$7 \frac{d}{d x} [\frac{1}{x}]$

Step 1.1.1.2

Rewrite

\frac{1}{x}

$\frac{1}{x}$ as

x^{- 1}

$x^{- 1}$ .

7 \frac{d}{d x} [x^{- 1}]

$7 \frac{d}{d x} [x^{- 1}]$

Step 1.1.1.3

Differentiate using the Power Rule which states that

\frac{d}{d x} [x^{n}]

$\frac{d}{d x} [x^{n}]$ is

n x^{n - 1}

$n x^{n - 1}$ where

n = - 1

$n = - 1$ .

7 (- x^{- 2})

$7 (- x^{- 2})$

Step 1.1.1.4

Multiply

- 1

$- 1$ by

7

$7$ .

- 7 x^{- 2}

$- 7 x^{- 2}$

Step 1.1.1.5

Simplify.

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Step 1.1.1.5.1

Rewrite the expression using the negative exponent rule

b^{- n} = \frac{1}{b^{n}}

$b^{- n} = \frac{1}{b^{n}}$ .

- 7 \frac{1}{x^{2}}

$- 7 \frac{1}{x^{2}}$

Step 1.1.1.5.2

Combine terms.

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Step 1.1.1.5.2.1

Combine

- 7

$- 7$ and

\frac{1}{x^{2}}

$\frac{1}{x^{2}}$ .

\frac{- 7}{x^{2}}

$\frac{- 7}{x^{2}}$

Step 1.1.1.5.2.2

Move the negative in front of the fraction.

$f' (x) = - \frac{7}{x^{2}}$

Step 1.1.2

The first derivative of

$f (x)$ with respect to

$x$ is

$- \frac{7}{x^{2}}$ .

$- \frac{7}{x^{2}}$

Step 1.2

Set the first derivative equal to

$0$ then solve the equation

$- \frac{7}{x^{2}} = 0$ .

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Step 1.2.1

Set the first derivative equal to

$0$ .

$- \frac{7}{x^{2}} = 0$

Step 1.2.2

Set the numerator equal to zero.

$7 = 0$

Step 1.2.3

Since

$7 \neq 0$ , there are no solutions.

No solution

Step 1.3

Find the values where the derivative is undefined.

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Step 1.3.1

Set the denominator in

$\frac{7}{x^{2}}$ equal to

$0$ to find where the expression is undefined.

$x^{2} = 0$

Step 1.3.2

Solve for

$x$ .

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Step 1.3.2.1

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

$x = \pm \sqrt{0}$

Step 1.3.2.2

Simplify

$\pm \sqrt{0}$ .

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Step 1.3.2.2.1

Rewrite

$0$ as

$0^{2}$ .

$x = \pm \sqrt{0^{2}}$

Step 1.3.2.2.2

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

$x = \pm 0$

Step 1.3.2.2.3

Plus or minus

$0$ is

$0$ .

$x = 0$

Step 1.4

Evaluate

$\frac{7}{x}$ at each

$x$ value where the derivative is

$0$ or undefined.

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Step 1.4.1

Evaluate at

$x = 0$ .

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Step 1.4.1.1

Substitute

$0$ for

$x$ .

$\frac{7}{0}$

Step 1.4.1.2

The expression contains a division by

$0$ . The expression is undefined.

Undefined

Step 1.5

There are no values of

$x$ in the domain of the original problem where the derivative is

$0$ or undefined.

No critical points found

Step 2

Evaluate at the included endpoints.

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Step 2.1

Evaluate at

$x = 7$ .

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Step 2.1.1

Substitute

$7$ for

$x$ .

$\frac{7}{7}$

Step 2.1.2

Divide

$7$ by

$7$ .

$1$

Step 2.2

List all of the points.

$(7, 1)$

Step 3

Since there is no value of

$x$ that makes the first derivative equal to

$0$ , there are no local extrema.

No Local Extrema

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:

$(7, 1)$

No absolute minimum

Step 5