Calculus Examples

$f (x) = 3 x - 36 x^{\frac{1}{3}}$

Step 1

Find the first derivative of the function.

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Step 1.1

By the Sum Rule, the derivative of $3 x - 36 x^{\frac{1}{3}}$ with respect to $x$ is $\frac{d}{d x} [3 x] + \frac{d}{d x} [- 36 x^{\frac{1}{3}}]$ .

$\frac{d}{d x} [3 x] + \frac{d}{d x} [- 36 x^{\frac{1}{3}}]$

Step 1.2

Evaluate $\frac{d}{d x} [3 x]$ .

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Step 1.2.1

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

$3 \frac{d}{d x} [x] + \frac{d}{d x} [- 36 x^{\frac{1}{3}}]$

Step 1.2.2

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

$3 \cdot 1 + \frac{d}{d x} [- 36 x^{\frac{1}{3}}]$

Step 1.2.3

Multiply $3$ by $1$ .

$3 + \frac{d}{d x} [- 36 x^{\frac{1}{3}}]$

Step 1.3

Evaluate $\frac{d}{d x} [- 36 x^{\frac{1}{3}}]$ .

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Step 1.3.1

Since $- 36$ is constant with respect to $x$ , the derivative of $- 36 x^{\frac{1}{3}}$ with respect to $x$ is $- 36 \frac{d}{d x} [x^{\frac{1}{3}}]$ .

$3 - 36 \frac{d}{d x} [x^{\frac{1}{3}}]$

Step 1.3.2

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = \frac{1}{3}$ .

$3 - 36 (\frac{1}{3} x^{\frac{1}{3} - 1})$

Step 1.3.3

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

$3 - 36 (\frac{1}{3} x^{\frac{1}{3} - 1 \cdot \frac{3}{3}})$

Step 1.3.4

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

$3 - 36 (\frac{1}{3} x^{\frac{1}{3} + \frac{- 1 \cdot 3}{3}})$

Step 1.3.5

Combine the numerators over the common denominator.

$3 - 36 (\frac{1}{3} x^{\frac{1 - 1 \cdot 3}{3}})$

Step 1.3.6

Simplify the numerator.

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Step 1.3.6.1

Multiply $- 1$ by $3$ .

$3 - 36 (\frac{1}{3} x^{\frac{1 - 3}{3}})$

Step 1.3.6.2

Subtract $3$ from $1$ .

$3 - 36 (\frac{1}{3} x^{\frac{- 2}{3}})$

Step 1.3.7

Move the negative in front of the fraction.

$3 - 36 (\frac{1}{3} x^{- \frac{2}{3}})$

Step 1.3.8

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

$3 - 36 \frac{x^{- \frac{2}{3}}}{3}$

Step 1.3.9

Combine $- 36$ and $\frac{x^{- \frac{2}{3}}}{3}$ .

$3 + \frac{- 36 x^{- \frac{2}{3}}}{3}$

Step 1.3.10

Move $x^{- \frac{2}{3}}$ to the denominator using the negative exponent rule $b^{- n} = \frac{1}{b^{n}}$ .

$3 + \frac{- 36}{3 x^{\frac{2}{3}}}$

Step 1.3.11

Factor $3$ out of $- 36$ .

$3 + \frac{3 \cdot - 12}{3 x^{\frac{2}{3}}}$

Step 1.3.12

Cancel the common factors.

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Step 1.3.12.1

Factor $3$ out of $3 x^{\frac{2}{3}}$ .

$3 + \frac{3 \cdot - 12}{3 (x^{\frac{2}{3}})}$

Step 1.3.12.2

Cancel the common factor.

$3 + \frac{3 \cdot - 12}{3 x^{\frac{2}{3}}}$

Step 1.3.12.3

Rewrite the expression.

$3 + \frac{- 12}{x^{\frac{2}{3}}}$

Step 1.3.13

Move the negative in front of the fraction.

$3 - \frac{12}{x^{\frac{2}{3}}}$

Step 2

Find the second derivative of the function.

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Step 2.1

Differentiate.

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Step 2.1.1

By the Sum Rule, the derivative of $3 - \frac{12}{x^{\frac{2}{3}}}$ with respect to $x$ is $\frac{d}{d x} [3] + \frac{d}{d x} [- \frac{12}{x^{\frac{2}{3}}}]$ .

$f'' (x) = \frac{d}{d x} (3) + \frac{d}{d x} (- \frac{12}{x^{\frac{2}{3}}})$

Step 2.1.2

Since $3$ is constant with respect to $x$ , the derivative of $3$ with respect to $x$ is $0$ .

$f'' (x) = 0 + \frac{d}{d x} (- \frac{12}{x^{\frac{2}{3}}})$

Step 2.2

Evaluate $\frac{d}{d x} [- \frac{12}{x^{\frac{2}{3}}}]$ .

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Step 2.2.1

Since $- 12$ is constant with respect to $x$ , the derivative of $- \frac{12}{x^{\frac{2}{3}}}$ with respect to $x$ is $- 12 \frac{d}{d x} [\frac{1}{x^{\frac{2}{3}}}]$ .

$f'' (x) = 0 - 12 \frac{d}{d x} \frac{1}{x^{\frac{2}{3}}}$

Step 2.2.2

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

$f'' (x) = 0 - 12 \frac{d}{d x} {(x^{\frac{2}{3}})}^{- 1}$

Step 2.2.3

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = x^{- 1}$ and $g (x) = x^{\frac{2}{3}}$ .

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Step 2.2.3.1

To apply the Chain Rule, set $u$ as $x^{\frac{2}{3}}$ .

$f'' (x) = 0 - 12 (\frac{d}{d u} (u^{- 1}) \frac{d}{d x} (x^{\frac{2}{3}}))$

Step 2.2.3.2

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

$f'' (x) = 0 - 12 (- u^{- 2} \frac{d}{d x} x^{\frac{2}{3}})$

Step 2.2.3.3

Replace all occurrences of $u$ with $x^{\frac{2}{3}}$ .

$f'' (x) = 0 - 12 (- {(x^{\frac{2}{3}})}^{- 2} \frac{d}{d x} x^{\frac{2}{3}})$

Step 2.2.4

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = \frac{2}{3}$ .

$f'' (x) = 0 - 12 (- {(x^{\frac{2}{3}})}^{- 2} (\frac{2}{3} x^{\frac{2}{3} - 1}))$

Step 2.2.5

Multiply the exponents in ${(x^{\frac{2}{3}})}^{- 2}$ .

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Step 2.2.5.1

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

$f'' (x) = 0 - 12 (- x^{\frac{2}{3} \cdot - 2} (\frac{2}{3} x^{\frac{2}{3} - 1}))$

Step 2.2.5.2

Multiply $\frac{2}{3} \cdot - 2$ .

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Step 2.2.5.2.1

Combine $\frac{2}{3}$ and $- 2$ .

$f'' (x) = 0 - 12 (- x^{\frac{2 \cdot - 2}{3}} (\frac{2}{3} x^{\frac{2}{3} - 1}))$

Step 2.2.5.2.2

Multiply $2$ by $- 2$ .

$f'' (x) = 0 - 12 (- x^{\frac{- 4}{3}} (\frac{2}{3} x^{\frac{2}{3} - 1}))$

Step 2.2.5.3

Move the negative in front of the fraction.

$f'' (x) = 0 - 12 (- x^{- \frac{4}{3}} (\frac{2}{3} x^{\frac{2}{3} - 1}))$

Step 2.2.6

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

$f'' (x) = 0 - 12 (- x^{- \frac{4}{3}} (\frac{2}{3} x^{\frac{2}{3} - 1 \cdot \frac{3}{3}}))$

Step 2.2.7

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

$f'' (x) = 0 - 12 (- x^{- \frac{4}{3}} (\frac{2}{3} x^{\frac{2}{3} + \frac{- 1 \cdot 3}{3}}))$

Step 2.2.8

Combine the numerators over the common denominator.

$f'' (x) = 0 - 12 (- x^{- \frac{4}{3}} (\frac{2}{3} x^{\frac{2 - 1 \cdot 3}{3}}))$

Step 2.2.9

Simplify the numerator.

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Step 2.2.9.1

Multiply $- 1$ by $3$ .

$f'' (x) = 0 - 12 (- x^{- \frac{4}{3}} (\frac{2}{3} x^{\frac{2 - 3}{3}}))$

Step 2.2.9.2

Subtract $3$ from $2$ .

$f'' (x) = 0 - 12 (- x^{- \frac{4}{3}} (\frac{2}{3} x^{\frac{- 1}{3}}))$

Step 2.2.10

Move the negative in front of the fraction.

$f'' (x) = 0 - 12 (- x^{- \frac{4}{3}} (\frac{2}{3} x^{- \frac{1}{3}}))$

Step 2.2.11

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

$f'' (x) = 0 - 12 (- x^{- \frac{4}{3}} \frac{2 x^{- \frac{1}{3}}}{3})$

Step 2.2.12

Combine $\frac{2 x^{- \frac{1}{3}}}{3}$ and $x^{- \frac{4}{3}}$ .

$f'' (x) = 0 - 12 (- \frac{2 x^{- \frac{1}{3}} x^{- \frac{4}{3}}}{3})$

Step 2.2.13

Multiply $x^{- \frac{1}{3}}$ by $x^{- \frac{4}{3}}$ by adding the exponents.

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Step 2.2.13.1

Move $x^{- \frac{4}{3}}$ .

$f'' (x) = 0 - 12 (- \frac{2 (x^{- \frac{4}{3}} x^{- \frac{1}{3}})}{3})$

Step 2.2.13.2

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

$f'' (x) = 0 - 12 (- \frac{2 x^{- \frac{4}{3} - \frac{1}{3}}}{3})$

Step 2.2.13.3

Combine the numerators over the common denominator.

$f'' (x) = 0 - 12 (- \frac{2 x^{\frac{- 4 - 1}{3}}}{3})$

Step 2.2.13.4

Subtract $1$ from $- 4$ .

$f'' (x) = 0 - 12 (- \frac{2 x^{\frac{- 5}{3}}}{3})$

Step 2.2.13.5

Move the negative in front of the fraction.

$f'' (x) = 0 - 12 (- \frac{2 x^{- \frac{5}{3}}}{3})$

Step 2.2.14

Move $x^{- \frac{5}{3}}$ to the denominator using the negative exponent rule $b^{- n} = \frac{1}{b^{n}}$ .

$f'' (x) = 0 - 12 (- \frac{2}{3 x^{\frac{5}{3}}})$

Step 2.2.15

Multiply $- 1$ by $- 12$ .

$f'' (x) = 0 + 12 (\frac{2}{3 x^{\frac{5}{3}}})$

Step 2.2.16

Combine $12$ and $\frac{2}{3 x^{\frac{5}{3}}}$ .

$f'' (x) = 0 + \frac{12 \cdot 2}{3 x^{\frac{5}{3}}}$

Step 2.2.17

Multiply $12$ by $2$ .

$f'' (x) = 0 + \frac{24}{3 x^{\frac{5}{3}}}$

Step 2.2.18

Factor $3$ out of $24$ .

$f'' (x) = 0 + \frac{3 \cdot 8}{3 x^{\frac{5}{3}}}$

Step 2.2.19

Cancel the common factors.

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Step 2.2.19.1

Factor $3$ out of $3 x^{\frac{5}{3}}$ .

$f'' (x) = 0 + \frac{3 \cdot 8}{3 (x^{\frac{5}{3}})}$

Step 2.2.19.2

Cancel the common factor.

$f'' (x) = 0 + \frac{3 \cdot 8}{3 x^{\frac{5}{3}}}$

Step 2.2.19.3

Rewrite the expression.

$f'' (x) = 0 + \frac{8}{x^{\frac{5}{3}}}$

Step 2.3

Add $0$ and $\frac{8}{x^{\frac{5}{3}}}$ .

$f'' (x) = \frac{8}{x^{\frac{5}{3}}}$

Step 3

To find the local maximum and minimum values of the function, set the derivative equal to $0$ and solve.

$3 - \frac{12}{x^{\frac{2}{3}}} = 0$

Step 4

Find the first derivative.

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Step 4.1

Find the first derivative.

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Step 4.1.1

By the Sum Rule, the derivative of $3 x - 36 x^{\frac{1}{3}}$ with respect to $x$ is $\frac{d}{d x} [3 x] + \frac{d}{d x} [- 36 x^{\frac{1}{3}}]$ .

$f' (x) = \frac{d}{d x} (3 x) + \frac{d}{d x} (- 36 x^{\frac{1}{3}})$

Step 4.1.2

Evaluate $\frac{d}{d x} [3 x]$ .

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Step 4.1.2.1

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

$f' (x) = 3 \frac{d}{d x} (x) + \frac{d}{d x} (- 36 x^{\frac{1}{3}})$

Step 4.1.2.2

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

$f' (x) = 3 \cdot 1 + \frac{d}{d x} (- 36 x^{\frac{1}{3}})$

Step 4.1.2.3

Multiply $3$ by $1$ .

$f' (x) = 3 + \frac{d}{d x} (- 36 x^{\frac{1}{3}})$

Step 4.1.3

Evaluate $\frac{d}{d x} [- 36 x^{\frac{1}{3}}]$ .

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Step 4.1.3.1

Since $- 36$ is constant with respect to $x$ , the derivative of $- 36 x^{\frac{1}{3}}$ with respect to $x$ is $- 36 \frac{d}{d x} [x^{\frac{1}{3}}]$ .

$f' (x) = 3 - 36 \frac{d}{d x} x^{\frac{1}{3}}$

Step 4.1.3.2

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = \frac{1}{3}$ .

$f' (x) = 3 - 36 (\frac{1}{3} x^{\frac{1}{3} - 1})$

Step 4.1.3.3

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

$f' (x) = 3 - 36 (\frac{1}{3} x^{\frac{1}{3} - 1 \cdot \frac{3}{3}})$

Step 4.1.3.4

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

$f' (x) = 3 - 36 (\frac{1}{3} x^{\frac{1}{3} + \frac{- 1 \cdot 3}{3}})$

Step 4.1.3.5

Combine the numerators over the common denominator.

$f' (x) = 3 - 36 (\frac{1}{3} x^{\frac{1 - 1 \cdot 3}{3}})$

Step 4.1.3.6

Simplify the numerator.

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Step 4.1.3.6.1

Multiply $- 1$ by $3$ .

$f' (x) = 3 - 36 (\frac{1}{3} x^{\frac{1 - 3}{3}})$

Step 4.1.3.6.2

Subtract $3$ from $1$ .

$f' (x) = 3 - 36 (\frac{1}{3} x^{\frac{- 2}{3}})$

Step 4.1.3.7

Move the negative in front of the fraction.

$f' (x) = 3 - 36 (\frac{1}{3} x^{- \frac{2}{3}})$

Step 4.1.3.8

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

$f' (x) = 3 - 36 \frac{x^{- \frac{2}{3}}}{3}$

Step 4.1.3.9

Combine $- 36$ and $\frac{x^{- \frac{2}{3}}}{3}$ .

$f' (x) = 3 + \frac{- 36 x^{- \frac{2}{3}}}{3}$

Step 4.1.3.10

Move $x^{- \frac{2}{3}}$ to the denominator using the negative exponent rule $b^{- n} = \frac{1}{b^{n}}$ .

$f' (x) = 3 + \frac{- 36}{3 x^{\frac{2}{3}}}$

Step 4.1.3.11

Factor $3$ out of $- 36$ .

$f' (x) = 3 + \frac{3 \cdot - 12}{3 x^{\frac{2}{3}}}$

Step 4.1.3.12

Cancel the common factors.

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Step 4.1.3.12.1

Factor $3$ out of $3 x^{\frac{2}{3}}$ .

$f' (x) = 3 + \frac{3 \cdot - 12}{3 (x^{\frac{2}{3}})}$

Step 4.1.3.12.2

Cancel the common factor.

$f' (x) = 3 + \frac{3 \cdot - 12}{3 x^{\frac{2}{3}}}$

Step 4.1.3.12.3

Rewrite the expression.

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

Step 4.1.3.13

Move the negative in front of the fraction.

$f' (x) = 3 - \frac{12}{x^{\frac{2}{3}}}$

Step 4.2

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

$3 - \frac{12}{x^{\frac{2}{3}}}$

Step 5

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

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Step 5.1

Set the first derivative equal to $0$ .

$3 - \frac{12}{x^{\frac{2}{3}}} = 0$

Step 5.2

Subtract $3$ from both sides of the equation.

$- \frac{12}{x^{\frac{2}{3}}} = - 3$

Step 5.3

Find the LCD of the terms in the equation.

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Step 5.3.1

Finding the LCD of a list of values is the same as finding the LCM of the denominators of those values.

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

Step 5.3.2

The LCM of one and any expression is the expression.

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

Step 5.4

Multiply each term in $- \frac{12}{x^{\frac{2}{3}}} = - 3$ by $x^{\frac{2}{3}}$ to eliminate the fractions.

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Step 5.4.1

Multiply each term in $- \frac{12}{x^{\frac{2}{3}}} = - 3$ by $x^{\frac{2}{3}}$ .

$- \frac{12}{x^{\frac{2}{3}}} x^{\frac{2}{3}} = - 3 x^{\frac{2}{3}}$

Step 5.4.2

Simplify the left side.

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Step 5.4.2.1

Cancel the common factor of $x^{\frac{2}{3}}$ .

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Step 5.4.2.1.1

Move the leading negative in $- \frac{12}{x^{\frac{2}{3}}}$ into the numerator.

$\frac{- 12}{x^{\frac{2}{3}}} x^{\frac{2}{3}} = - 3 x^{\frac{2}{3}}$

Step 5.4.2.1.2

Cancel the common factor.

$\frac{- 12}{x^{\frac{2}{3}}} x^{\frac{2}{3}} = - 3 x^{\frac{2}{3}}$

Step 5.4.2.1.3

Rewrite the expression.

$- 12 = - 3 x^{\frac{2}{3}}$

Step 5.5

Solve the equation.

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Step 5.5.1

Rewrite the equation as $- 3 x^{\frac{2}{3}} = - 12$ .

$- 3 x^{\frac{2}{3}} = - 12$

Step 5.5.2

Divide each term in $- 3 x^{\frac{2}{3}} = - 12$ by $- 3$ and simplify.

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Step 5.5.2.1

Divide each term in $- 3 x^{\frac{2}{3}} = - 12$ by $- 3$ .

$\frac{- 3 x^{\frac{2}{3}}}{- 3} = \frac{- 12}{- 3}$

Step 5.5.2.2

Simplify the left side.

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Step 5.5.2.2.1

Cancel the common factor.

$\frac{- 3 x^{\frac{2}{3}}}{- 3} = \frac{- 12}{- 3}$

Step 5.5.2.2.2

Divide $x^{\frac{2}{3}}$ by $1$ .

$x^{\frac{2}{3}} = \frac{- 12}{- 3}$

Step 5.5.2.3

Simplify the right side.

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Step 5.5.2.3.1

Divide $- 12$ by $- 3$ .

$x^{\frac{2}{3}} = 4$

Step 5.5.3

Raise each side of the equation to the power of $\frac{3}{2}$ to eliminate the fractional exponent on the left side.

${(x^{\frac{2}{3}})}^{\frac{3}{2}} = \pm 4^{\frac{3}{2}}$

Step 5.5.4

Simplify the exponent.

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Step 5.5.4.1

Simplify the left side.

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Step 5.5.4.1.1

Simplify ${(x^{\frac{2}{3}})}^{\frac{3}{2}}$ .

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Step 5.5.4.1.1.1

Multiply the exponents in ${(x^{\frac{2}{3}})}^{\frac{3}{2}}$ .

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Step 5.5.4.1.1.1.1

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

$x^{\frac{2}{3} \cdot \frac{3}{2}} = \pm 4^{\frac{3}{2}}$

Step 5.5.4.1.1.1.2

Cancel the common factor of $2$ .

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Step 5.5.4.1.1.1.2.1

Cancel the common factor.

$x^{\frac{2}{3} \cdot \frac{3}{2}} = \pm 4^{\frac{3}{2}}$

Step 5.5.4.1.1.1.2.2

Rewrite the expression.

$x^{\frac{1}{3} \cdot 3} = \pm 4^{\frac{3}{2}}$

Step 5.5.4.1.1.1.3

Cancel the common factor of $3$ .

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Step 5.5.4.1.1.1.3.1

Cancel the common factor.

$x^{\frac{1}{3} \cdot 3} = \pm 4^{\frac{3}{2}}$

Step 5.5.4.1.1.1.3.2

Rewrite the expression.

$x^{1} = \pm 4^{\frac{3}{2}}$

Step 5.5.4.1.1.2

Simplify.

$x = \pm 4^{\frac{3}{2}}$

Step 5.5.4.2

Simplify the right side.

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Step 5.5.4.2.1

Simplify $\pm 4^{\frac{3}{2}}$ .

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Step 5.5.4.2.1.1

Simplify the expression.

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Step 5.5.4.2.1.1.1

Rewrite $4$ as $2^{2}$ .

$x = \pm {(2^{2})}^{\frac{3}{2}}$

Step 5.5.4.2.1.1.2

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

$x = \pm 2^{2 (\frac{3}{2})}$

Step 5.5.4.2.1.2

Cancel the common factor of $2$ .

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Step 5.5.4.2.1.2.1

Cancel the common factor.

$x = \pm 2^{2 (\frac{3}{2})}$

Step 5.5.4.2.1.2.2

Rewrite the expression.

$x = \pm 2^{3}$

Step 5.5.4.2.1.3

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

$x = \pm 8$

Step 5.5.5

The complete solution is the result of both the positive and negative portions of the solution.

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Step 5.5.5.1

First, use the positive value of the $\pm$ to find the first solution.

$x = 8$

Step 5.5.5.2

Next, use the negative value of the $\pm$ to find the second solution.

$x = - 8$

Step 5.5.5.3

The complete solution is the result of both the positive and negative portions of the solution.

$x = 8, - 8$

Step 6

Find the values where the derivative is undefined.

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Step 6.1

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

$3 - \frac{12}{\sqrt[3]{x^{2}}}$

Step 6.2

Set the denominator in $\frac{12}{\sqrt[3]{x^{2}}}$ equal to $0$ to find where the expression is undefined.

$\sqrt[3]{x^{2}} = 0$

Step 6.3

Solve for $x$ .

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Step 6.3.1

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

${\sqrt[3]{x^{2}}}^{3} = 0^{3}$

Step 6.3.2

Simplify each side of the equation.

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Step 6.3.2.1

Use $\sqrt[n]{a^{x}} = a^{\frac{x}{n}}$ to rewrite $\sqrt[3]{x^{2}}$ as $x^{\frac{2}{3}}$ .

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

Step 6.3.2.2

Simplify the left side.

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Step 6.3.2.2.1

Multiply the exponents in ${(x^{\frac{2}{3}})}^{3}$ .

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Step 6.3.2.2.1.1

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

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

Step 6.3.2.2.1.2

Cancel the common factor of $3$ .

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Step 6.3.2.2.1.2.1

Cancel the common factor.

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

Step 6.3.2.2.1.2.2

Rewrite the expression.

$x^{2} = 0^{3}$

Step 6.3.2.3

Simplify the right side.

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Step 6.3.2.3.1

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

$x^{2} = 0$

Step 6.3.3

Solve for $x$ .

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Step 6.3.3.1

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

$x = \pm \sqrt{0}$

Step 6.3.3.2

Simplify $\pm \sqrt{0}$ .

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Step 6.3.3.2.1

Rewrite $0$ as $0^{2}$ .

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

Step 6.3.3.2.2

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

$x = \pm 0$

Step 6.3.3.2.3

Plus or minus $0$ is $0$ .

$x = 0$

Step 7

Critical points to evaluate.

$x = 8, - 8, 0$

Step 8

Evaluate the second derivative at $x = 8$ . If the second derivative is positive, then this is a local minimum. If it is negative, then this is a local maximum.

$\frac{8}{{(8)}^{\frac{5}{3}}}$

Step 9

Evaluate the second derivative.

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Step 9.1

Move $8^{1}$ to the denominator using the negative exponent rule $b^{n} = \frac{1}{b^{- n}}$ .

$\frac{1}{{(8)}^{\frac{5}{3}} \cdot 8^{- 1}}$

Step 9.2

Multiply ${(8)}^{\frac{5}{3}}$ by $8^{- 1}$ by adding the exponents.

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Step 9.2.1

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

$\frac{1}{8^{\frac{5}{3} - 1}}$

Step 9.2.2

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

$\frac{1}{8^{\frac{5}{3} - 1 \cdot \frac{3}{3}}}$

Step 9.2.3

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

$\frac{1}{8^{\frac{5}{3} + \frac{- 1 \cdot 3}{3}}}$

Step 9.2.4

Combine the numerators over the common denominator.

$\frac{1}{8^{\frac{5 - 1 \cdot 3}{3}}}$

Step 9.2.5

Simplify the numerator.

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Step 9.2.5.1

Multiply $- 1$ by $3$ .

$\frac{1}{8^{\frac{5 - 3}{3}}}$

Step 9.2.5.2

Subtract $3$ from $5$ .

$\frac{1}{8^{\frac{2}{3}}}$

Step 9.3

Simplify the denominator.

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Step 9.3.1

Rewrite $8$ as $2^{3}$ .

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

Step 9.3.2

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

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

Step 9.3.3

Cancel the common factor of $3$ .

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Step 9.3.3.1

Cancel the common factor.

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

Step 9.3.3.2

Rewrite the expression.

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

Step 9.3.4

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

$\frac{1}{4}$

Step 10

$x = 8$ is a local minimum because the value of the second derivative is positive. This is referred to as the second derivative test.

$x = 8$ is a local minimum

Step 11

Find the y-value when $x = 8$ .

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Step 11.1

Replace the variable $x$ with $8$ in the expression.

$f (8) = 3 (8) - 36 {(8)}^{\frac{1}{3}}$

Step 11.2

Simplify the result.

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Step 11.2.1

Simplify each term.

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Step 11.2.1.1

Multiply $3$ by $8$ .

$f (8) = 24 - 36 {(8)}^{\frac{1}{3}}$

Step 11.2.1.2

Rewrite $8$ as $2^{3}$ .

$f (8) = 24 - 36 {(2^{3})}^{\frac{1}{3}}$

Step 11.2.1.3

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

$f (8) = 24 - 36 \cdot 2^{3 (\frac{1}{3})}$

Step 11.2.1.4

Cancel the common factor of $3$ .

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Step 11.2.1.4.1

Cancel the common factor.

$f (8) = 24 - 36 \cdot 2^{3 (\frac{1}{3})}$

Step 11.2.1.4.2

Rewrite the expression.

$f (8) = 24 - 36 \cdot 2$

Step 11.2.1.5

Evaluate the exponent.

$f (8) = 24 - 36 \cdot 2$

Step 11.2.1.6

Multiply $- 36$ by $2$ .

$f (8) = 24 - 72$

Step 11.2.2

Subtract $72$ from $24$ .

$f (8) = - 48$

Step 11.2.3

The final answer is $- 48$ .

$y = - 48$

Step 12

Evaluate the second derivative at $x = - 8$ . If the second derivative is positive, then this is a local minimum. If it is negative, then this is a local maximum.

$\frac{8}{{(- 8)}^{\frac{5}{3}}}$

Step 13

Evaluate the second derivative.

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Step 13.1

Simplify the denominator.

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Step 13.1.1

Rewrite $- 8$ as ${(- 2)}^{3}$ .

$\frac{8}{{({(- 2)}^{3})}^{\frac{5}{3}}}$

Step 13.1.2

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

$\frac{8}{{(- 2)}^{3 (\frac{5}{3})}}$

Step 13.1.3

Cancel the common factor of $3$ .

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Step 13.1.3.1

Cancel the common factor.

$\frac{8}{{(- 2)}^{3 (\frac{5}{3})}}$

Step 13.1.3.2

Rewrite the expression.

$\frac{8}{{(- 2)}^{5}}$

Step 13.1.4

Raise $- 2$ to the power of $5$ .

$\frac{8}{- 32}$

Step 13.2

Reduce the expression by cancelling the common factors.

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Step 13.2.1

Cancel the common factor of $8$ and $- 32$ .

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Step 13.2.1.1

Factor $8$ out of $8$ .

$\frac{8 (1)}{- 32}$

Step 13.2.1.2

Cancel the common factors.

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Step 13.2.1.2.1

Factor $8$ out of $- 32$ .

$\frac{8 \cdot 1}{8 \cdot - 4}$

Step 13.2.1.2.2

Cancel the common factor.

$\frac{8 \cdot 1}{8 \cdot - 4}$

Step 13.2.1.2.3

Rewrite the expression.

$\frac{1}{- 4}$

Step 13.2.2

Move the negative in front of the fraction.

$- \frac{1}{4}$

Step 14

$x = - 8$ is a local maximum because the value of the second derivative is negative. This is referred to as the second derivative test.

$x = - 8$ is a local maximum

Step 15

Find the y-value when $x = - 8$ .

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Step 15.1

Replace the variable $x$ with $- 8$ in the expression.

$f (- 8) = 3 (- 8) - 36 {(- 8)}^{\frac{1}{3}}$

Step 15.2

Simplify the result.

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Step 15.2.1

Simplify each term.

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Step 15.2.1.1

Multiply $3$ by $- 8$ .

$f (- 8) = - 24 - 36 {(- 8)}^{\frac{1}{3}}$

Step 15.2.1.2

Rewrite $- 8$ as ${(- 2)}^{3}$ .

$f (- 8) = - 24 - 36 {({(- 2)}^{3})}^{\frac{1}{3}}$

Step 15.2.1.3

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

$f (- 8) = - 24 - 36 {(- 2)}^{3 (\frac{1}{3})}$

Step 15.2.1.4

Cancel the common factor of $3$ .

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Step 15.2.1.4.1

Cancel the common factor.

$f (- 8) = - 24 - 36 {(- 2)}^{3 (\frac{1}{3})}$

Step 15.2.1.4.2

Rewrite the expression.

$f (- 8) = - 24 - 36 \cdot - 2$

Step 15.2.1.5

Evaluate the exponent.

$f (- 8) = - 24 - 36 \cdot - 2$

Step 15.2.1.6

Multiply $- 36$ by $- 2$ .

$f (- 8) = - 24 + 72$

Step 15.2.2

Add $- 24$ and $72$ .

$f (- 8) = 48$

Step 15.2.3

The final answer is $48$ .

$y = 48$

Step 16

Evaluate the second derivative at $x = 0$ . If the second derivative is positive, then this is a local minimum. If it is negative, then this is a local maximum.

$\frac{8}{{(0)}^{\frac{5}{3}}}$

Step 17

Evaluate the second derivative.

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Step 17.1

Simplify the expression.

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Step 17.1.1

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

$\frac{8}{{(0^{3})}^{\frac{5}{3}}}$

Step 17.1.2

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

$\frac{8}{0^{3 (\frac{5}{3})}}$

Step 17.2

Cancel the common factor of $3$ .

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Step 17.2.1

Cancel the common factor.

$\frac{8}{0^{3 (\frac{5}{3})}}$

Step 17.2.2

Rewrite the expression.

$\frac{8}{0^{5}}$

Step 17.3

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

$\frac{8}{0}$

Step 17.4

The expression contains a division by $0$ . The expression is undefined.

Undefined

Step 18

Since there is at least one point with $0$ or undefined second derivative, apply the first derivative test.

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Step 18.1

Split $(- \infty, \infty)$ into separate intervals around the $x$ values that make the first derivative $0$ or undefined.

$(- \infty, - 8) \cup (- 8, 0) \cup (0, 8) \cup (8, \infty)$

Step 18.2

Substitute any number, such as $- 10$ , from the interval $(- \infty, - 8)$ in the first derivative $3 - \frac{12}{x^{\frac{2}{3}}}$ to check if the result is negative or positive.

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Step 18.2.1

Replace the variable $x$ with $- 10$ in the expression.

$f' (- 10) = 3 - \frac{12}{{(- 10)}^{\frac{2}{3}}}$

Step 18.2.2

The final answer is $3 - \frac{12}{{(- 10)}^{\frac{2}{3}}}$ .

$3 - \frac{12}{{(- 10)}^{\frac{2}{3}}}$

Step 18.3

Substitute any number, such as $- 4$ , from the interval $(- 8, 0)$ in the first derivative $3 - \frac{12}{x^{\frac{2}{3}}}$ to check if the result is negative or positive.

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Step 18.3.1

Replace the variable $x$ with $- 4$ in the expression.

$f' (- 4) = 3 - \frac{12}{{(- 4)}^{\frac{2}{3}}}$

Step 18.3.2

The final answer is $3 - \frac{12}{{(- 4)}^{\frac{2}{3}}}$ .

$3 - \frac{12}{{(- 4)}^{\frac{2}{3}}}$

Step 18.4

Substitute any number, such as $4$ , from the interval $(0, 8)$ in the first derivative $3 - \frac{12}{x^{\frac{2}{3}}}$ to check if the result is negative or positive.

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Step 18.4.1

Replace the variable $x$ with $4$ in the expression.

$f' (4) = 3 - \frac{12}{{(4)}^{\frac{2}{3}}}$

Step 18.4.2

Simplify the result.

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Step 18.4.2.1

Remove parentheses.

$f' (4) = 3 - \frac{12}{4^{\frac{2}{3}}}$

Step 18.4.2.2

The final answer is $3 - \frac{12}{4^{\frac{2}{3}}}$ .

$3 - \frac{12}{4^{\frac{2}{3}}}$

Step 18.5

Substitute any number, such as $10$ , from the interval $(8, \infty)$ in the first derivative $3 - \frac{12}{x^{\frac{2}{3}}}$ to check if the result is negative or positive.

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Step 18.5.1

Replace the variable $x$ with $10$ in the expression.

$f' (10) = 3 - \frac{12}{{(10)}^{\frac{2}{3}}}$

Step 18.5.2

Simplify the result.

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Step 18.5.2.1

Remove parentheses.

$f' (10) = 3 - \frac{12}{10^{\frac{2}{3}}}$

Step 18.5.2.2

The final answer is $3 - \frac{12}{10^{\frac{2}{3}}}$ .

$3 - \frac{12}{10^{\frac{2}{3}}}$

Step 18.6

Since the first derivative changed signs from positive to negative around $x = - 8$ , then $x = - 8$ is a local maximum.

$x = - 8$ is a local maximum

Step 18.7

Since the first derivative did not change signs around $x = 0$ , this is not a local maximum or minimum.

Not a local maximum or minimum

Step 18.8

Since the first derivative changed signs from negative to positive around $x = 8$ , then $x = 8$ is a local minimum.

$x = 8$ is a local minimum

Step 18.9

These are the local extrema for $f (x) = 3 x - 36 x^{\frac{1}{3}}$ .

$x = - 8$ is a local maximum

$x = 8$ is a local minimum

$x = - 8$ is a local maximum

$x = 8$ is a local minimum

Step 19