Calculus Examples

$f (x) = 3 x^{\frac{2}{3}}$ , $[- 27, 27]$

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 $3$ is constant with respect to $x$ , the derivative of $3 x^{\frac{2}{3}}$ with respect to $x$ is $3 \frac{d}{d x} [x^{\frac{2}{3}}]$ .

$3 \frac{d}{d x} [x^{\frac{2}{3}}]$

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 $n = \frac{2}{3}$ .

$3 (\frac{2}{3} x^{\frac{2}{3} - 1})$

Step 1.1.1.3

To write $- 1$ as a fraction with a common denominator, multiply by $\frac{3}{3}$ .

$3 (\frac{2}{3} x^{\frac{2}{3} - 1 \cdot \frac{3}{3}})$

Step 1.1.1.4

Combine $- 1$ and $\frac{3}{3}$ .

$3 (\frac{2}{3} x^{\frac{2}{3} + \frac{- 1 \cdot 3}{3}})$

Step 1.1.1.5

Combine the numerators over the common denominator.

$3 (\frac{2}{3} x^{\frac{2 - 1 \cdot 3}{3}})$

Step 1.1.1.6

Simplify the numerator.

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Step 1.1.1.6.1

Multiply $- 1$ by $3$ .

$3 (\frac{2}{3} x^{\frac{2 - 3}{3}})$

Step 1.1.1.6.2

Subtract $3$ from $2$ .

$3 (\frac{2}{3} x^{\frac{- 1}{3}})$

Step 1.1.1.7

Move the negative in front of the fraction.

$3 (\frac{2}{3} x^{- \frac{1}{3}})$

Step 1.1.1.8

Combine $\frac{2}{3}$ and $x^{- \frac{1}{3}}$ .

$3 \frac{2 x^{- \frac{1}{3}}}{3}$

Step 1.1.1.9

Combine $3$ and $\frac{2 x^{- \frac{1}{3}}}{3}$ .

$\frac{3 (2 x^{- \frac{1}{3}})}{3}$

Step 1.1.1.10

Multiply.

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Step 1.1.1.10.1

Multiply $2$ by $3$ .

$\frac{6 x^{- \frac{1}{3}}}{3}$

Step 1.1.1.10.2

Move $x^{- \frac{1}{3}}$ to the denominator using the negative exponent rule $b^{- n} = \frac{1}{b^{n}}$ .

$\frac{6}{3 x^{\frac{1}{3}}}$

Step 1.1.1.11

Factor $3$ out of $6$ .

$\frac{3 \cdot 2}{3 x^{\frac{1}{3}}}$

Step 1.1.1.12

Cancel the common factors.

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Step 1.1.1.12.1

Factor $3$ out of $3 x^{\frac{1}{3}}$ .

$\frac{3 \cdot 2}{3 (x^{\frac{1}{3}})}$

Step 1.1.1.12.2

Cancel the common factor.

$\frac{3 \cdot 2}{3 x^{\frac{1}{3}}}$

Step 1.1.1.12.3

Rewrite the expression.

$f' (x) = \frac{2}{x^{\frac{1}{3}}}$

Step 1.1.2

The first derivative of $f (x)$ with respect to $x$ is $\frac{2}{x^{\frac{1}{3}}}$ .

$\frac{2}{x^{\frac{1}{3}}}$

Step 1.2

Set the first derivative equal to $0$ then solve the equation $\frac{2}{x^{\frac{1}{3}}} = 0$ .

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Step 1.2.1

Set the first derivative equal to $0$ .

$\frac{2}{x^{\frac{1}{3}}} = 0$

Step 1.2.2

Set the numerator equal to zero.

$2 = 0$

Step 1.2.3

Since $2 \neq 0$ , 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

Convert expressions with fractional exponents to radicals.

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Step 1.3.1.1

Apply the rule $x^{\frac{m}{n}} = \sqrt[n]{x^{m}}$ to rewrite the exponentiation as a radical.

$\frac{2}{\sqrt[3]{x^{1}}}$

Step 1.3.1.2

Anything raised to $1$ is the base itself.

$\frac{2}{\sqrt[3]{x}}$

Step 1.3.2

Set the denominator in $\frac{2}{\sqrt[3]{x}}$ equal to $0$ to find where the expression is undefined.

$\sqrt[3]{x} = 0$

Step 1.3.3

Solve for $x$ .

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Step 1.3.3.1

To remove the radical on the left side of the equation, cube both sides of the equation.

${\sqrt[3]{x}}^{3} = 0^{3}$

Step 1.3.3.2

Simplify each side of the equation.

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Step 1.3.3.2.1

Use $\sqrt[n]{a^{x}} = a^{\frac{x}{n}}$ to rewrite $\sqrt[3]{x}$ as $x^{\frac{1}{3}}$ .

${(x^{\frac{1}{3}})}^{3} = 0^{3}$

Step 1.3.3.2.2

Simplify the left side.

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Step 1.3.3.2.2.1

Simplify ${(x^{\frac{1}{3}})}^{3}$ .

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Step 1.3.3.2.2.1.1

Multiply the exponents in ${(x^{\frac{1}{3}})}^{3}$ .

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Step 1.3.3.2.2.1.1.1

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$x^{\frac{1}{3} \cdot 3} = 0^{3}$

Step 1.3.3.2.2.1.1.2

Cancel the common factor of $3$ .

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Step 1.3.3.2.2.1.1.2.1

Cancel the common factor.

$x^{\frac{1}{3} \cdot 3} = 0^{3}$

Step 1.3.3.2.2.1.1.2.2

Rewrite the expression.

$x^{1} = 0^{3}$

Step 1.3.3.2.2.1.2

Simplify.

$x = 0^{3}$

Step 1.3.3.2.3

Simplify the right side.

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Step 1.3.3.2.3.1

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

$x = 0$

Step 1.4

Evaluate $3 x^{\frac{2}{3}}$ 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 $x$ .

$3 {(0)}^{\frac{2}{3}}$

Step 1.4.1.2

Simplify.

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Step 1.4.1.2.1

Simplify the expression.

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Step 1.4.1.2.1.1

Rewrite $0$ as $0^{3}$ .

$3 {(0^{3})}^{\frac{2}{3}}$

Step 1.4.1.2.1.2

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$3 \cdot 0^{3 (\frac{2}{3})}$

Step 1.4.1.2.2

Cancel the common factor of $3$ .

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Step 1.4.1.2.2.1

Cancel the common factor.

$3 \cdot 0^{3 (\frac{2}{3})}$

Step 1.4.1.2.2.2

Rewrite the expression.

$3 \cdot 0^{2}$

Step 1.4.1.2.3

Simplify the expression.

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Step 1.4.1.2.3.1

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

$3 \cdot 0$

Step 1.4.1.2.3.2

Multiply $3$ by $0$ .

$0$

Step 1.4.2

List all of the points.

$(0, 0)$

Step 2

Evaluate at the included endpoints.

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Step 2.1

Evaluate at $x = - 27$ .

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Step 2.1.1

Substitute $- 27$ for $x$ .

$3 {(- 27)}^{\frac{2}{3}}$

Step 2.1.2

Simplify.

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Step 2.1.2.1

Simplify the expression.

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Step 2.1.2.1.1

Rewrite $- 27$ as ${(- 3)}^{3}$ .

$3 {({(- 3)}^{3})}^{\frac{2}{3}}$

Step 2.1.2.1.2

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$3 {(- 3)}^{3 (\frac{2}{3})}$

Step 2.1.2.2

Cancel the common factor of $3$ .

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Step 2.1.2.2.1

Cancel the common factor.

$3 {(- 3)}^{3 (\frac{2}{3})}$

Step 2.1.2.2.2

Rewrite the expression.

$3 {(- 3)}^{2}$

Step 2.1.2.3

Simplify the expression.

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Step 2.1.2.3.1

Raise $- 3$ to the power of $2$ .

$3 \cdot 9$

Step 2.1.2.3.2

Multiply $3$ by $9$ .

$27$

Step 2.2

Evaluate at $x = 27$ .

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Step 2.2.1

Substitute $27$ for $x$ .

$3 {(27)}^{\frac{2}{3}}$

Step 2.2.2

Simplify.

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Step 2.2.2.1

Simplify the expression.

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Step 2.2.2.1.1

Rewrite $27$ as $3^{3}$ .

$3 {(3^{3})}^{\frac{2}{3}}$

Step 2.2.2.1.2

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$3 \cdot 3^{3 (\frac{2}{3})}$

Step 2.2.2.2

Cancel the common factor of $3$ .

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Step 2.2.2.2.1

Cancel the common factor.

$3 \cdot 3^{3 (\frac{2}{3})}$

Step 2.2.2.2.2

Rewrite the expression.

$3 \cdot 3^{2}$

Step 2.2.2.3

Simplify the expression.

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Step 2.2.2.3.1

Raise $3$ to the power of $2$ .

$3 \cdot 9$

Step 2.2.2.3.2

Multiply $3$ by $9$ .

$27$

Step 2.3

List all of the points.

$(- 27, 27), (27, 27)$

Step 3

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: $(- 27, 27), (27, 27)$

Absolute Minimum: $(0, 0)$

Step 4