Precalculus Examples

$f (x) = 2 \sqrt[3]{x} - 5$

Step 1

Write $f (x) = 2 \sqrt[3]{x} - 5$ as an equation.

$y = 2 \sqrt[3]{x} - 5$

Step 2

Interchange the variables.

$x = 2 \sqrt[3]{y} - 5$

Step 3

Solve for $y$ .

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Step 3.1

Rewrite the equation as $2 \sqrt[3]{y} - 5 = x$ .

$2 \sqrt[3]{y} - 5 = x$

Step 3.2

Add $5$ to both sides of the equation.

$2 \sqrt[3]{y} = x + 5$

Step 3.3

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

${(2 \sqrt[3]{y})}^{3} = {(x + 5)}^{3}$

Step 3.4

Simplify each side of the equation.

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Step 3.4.1

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

${(2 y^{\frac{1}{3}})}^{3} = {(x + 5)}^{3}$

Step 3.4.2

Simplify the left side.

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Step 3.4.2.1

Simplify ${(2 y^{\frac{1}{3}})}^{3}$ .

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Step 3.4.2.1.1

Apply the product rule to $2 y^{\frac{1}{3}}$ .

$2^{3} {(y^{\frac{1}{3}})}^{3} = {(x + 5)}^{3}$

Step 3.4.2.1.2

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

$8 {(y^{\frac{1}{3}})}^{3} = {(x + 5)}^{3}$

Step 3.4.2.1.3

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

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Step 3.4.2.1.3.1

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

$8 y^{\frac{1}{3} \cdot 3} = {(x + 5)}^{3}$

Step 3.4.2.1.3.2

Cancel the common factor of $3$ .

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Step 3.4.2.1.3.2.1

Cancel the common factor.

$8 y^{\frac{1}{3} \cdot 3} = {(x + 5)}^{3}$

Step 3.4.2.1.3.2.2

Rewrite the expression.

$8 y^{1} = {(x + 5)}^{3}$

Step 3.4.2.1.4

Simplify.

$8 y = {(x + 5)}^{3}$

Step 3.4.3

Simplify the right side.

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Step 3.4.3.1

Simplify ${(x + 5)}^{3}$ .

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Step 3.4.3.1.1

Use the Binomial Theorem.

$8 y = x^{3} + 3 x^{2} \cdot 5 + 3 x \cdot 5^{2} + 5^{3}$

Step 3.4.3.1.2

Simplify each term.

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Step 3.4.3.1.2.1

Multiply $5$ by $3$ .

$8 y = x^{3} + 15 x^{2} + 3 x \cdot 5^{2} + 5^{3}$

Step 3.4.3.1.2.2

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

$8 y = x^{3} + 15 x^{2} + 3 x \cdot 25 + 5^{3}$

Step 3.4.3.1.2.3

Multiply $25$ by $3$ .

$8 y = x^{3} + 15 x^{2} + 75 x + 5^{3}$

Step 3.4.3.1.2.4

Raise $5$ to the power of $3$ .

$8 y = x^{3} + 15 x^{2} + 75 x + 125$

Step 3.5

Divide each term in $8 y = x^{3} + 15 x^{2} + 75 x + 125$ by $8$ and simplify.

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Step 3.5.1

Divide each term in $8 y = x^{3} + 15 x^{2} + 75 x + 125$ by $8$ .

$\frac{8 y}{8} = \frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}$

Step 3.5.2

Simplify the left side.

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Step 3.5.2.1

Cancel the common factor of $8$ .

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Step 3.5.2.1.1

Cancel the common factor.

$\frac{8 y}{8} = \frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}$

Step 3.5.2.1.2

Divide $y$ by $1$ .

$y = \frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}$

Step 4

Replace $y$ with $f^{- 1} (x)$ to show the final answer.

$f^{- 1} (x) = \frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}$

Step 5

Verify if $f^{- 1} (x) = \frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}$ is the inverse of $f (x) = 2 \sqrt[3]{x} - 5$ .

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Step 5.1

To verify the inverse, check if $f^{- 1} (f (x)) = x$ and $f (f^{- 1} (x)) = x$ .

Step 5.2

Evaluate $f^{- 1} (f (x))$ .

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Step 5.2.1

Set up the composite result function.

$f^{- 1} (f (x))$

Step 5.2.2

Evaluate $f^{- 1} (2 \sqrt[3]{x} - 5)$ by substituting in the value of $f$ into $f^{- 1}$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{{(2 \sqrt[3]{x} - 5)}^{3}}{8} + \frac{15 {(2 \sqrt[3]{x} - 5)}^{2}}{8} + \frac{75 (2 \sqrt[3]{x} - 5)}{8} + \frac{125}{8}$

Step 5.2.3

Combine the numerators over the common denominator.

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{{(2 \sqrt[3]{x} - 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4

Simplify each term.

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Step 5.2.4.1

Use the Binomial Theorem.

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{{(2 \sqrt[3]{x})}^{3} + 3 {(2 \sqrt[3]{x})}^{2} \cdot - 5 + 3 (2 \sqrt[3]{x}) {(- 5)}^{2} + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2

Simplify each term.

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Step 5.2.4.2.1

Apply the product rule to $2 \sqrt[3]{x}$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{2^{3} {\sqrt[3]{x}}^{3} + 3 {(2 \sqrt[3]{x})}^{2} \cdot - 5 + 3 (2 \sqrt[3]{x}) {(- 5)}^{2} + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2.2

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

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 {\sqrt[3]{x}}^{3} + 3 {(2 \sqrt[3]{x})}^{2} \cdot - 5 + 3 (2 \sqrt[3]{x}) {(- 5)}^{2} + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2.3

Rewrite ${\sqrt[3]{x}}^{3}$ as $x$ .

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Step 5.2.4.2.3.1

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

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 {(x^{\frac{1}{3}})}^{3} + 3 {(2 \sqrt[3]{x})}^{2} \cdot - 5 + 3 (2 \sqrt[3]{x}) {(- 5)}^{2} + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2.3.2

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

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x^{\frac{1}{3} \cdot 3} + 3 {(2 \sqrt[3]{x})}^{2} \cdot - 5 + 3 (2 \sqrt[3]{x}) {(- 5)}^{2} + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2.3.3

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

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x^{\frac{3}{3}} + 3 {(2 \sqrt[3]{x})}^{2} \cdot - 5 + 3 (2 \sqrt[3]{x}) {(- 5)}^{2} + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2.3.4

Cancel the common factor of $3$ .

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Step 5.2.4.2.3.4.1

Cancel the common factor.

Step 5.2.4.2.3.4.2

Rewrite the expression.

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x + 3 {(2 \sqrt[3]{x})}^{2} \cdot - 5 + 3 (2 \sqrt[3]{x}) {(- 5)}^{2} + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2.3.5

Simplify.

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x + 3 {(2 \sqrt[3]{x})}^{2} \cdot - 5 + 3 (2 \sqrt[3]{x}) {(- 5)}^{2} + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2.4

Apply the product rule to $2 \sqrt[3]{x}$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x + 3 (2^{2} {\sqrt[3]{x}}^{2}) \cdot - 5 + 3 (2 \sqrt[3]{x}) {(- 5)}^{2} + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2.5

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

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x + 3 (4 {\sqrt[3]{x}}^{2}) \cdot - 5 + 3 (2 \sqrt[3]{x}) {(- 5)}^{2} + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2.6

Rewrite ${\sqrt[3]{x}}^{2}$ as $\sqrt[3]{x^{2}}$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x + 3 (4 \sqrt[3]{x^{2}}) \cdot - 5 + 3 (2 \sqrt[3]{x}) {(- 5)}^{2} + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2.7

Multiply $4$ by $3$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x + 12 \sqrt[3]{x^{2}} \cdot - 5 + 3 (2 \sqrt[3]{x}) {(- 5)}^{2} + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2.8

Multiply $- 5$ by $12$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 3 (2 \sqrt[3]{x}) {(- 5)}^{2} + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2.9

Multiply $2$ by $3$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 6 \sqrt[3]{x} {(- 5)}^{2} + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2.10

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

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 6 \sqrt[3]{x} \cdot 25 + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2.11

Multiply $25$ by $6$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} + {(- 5)}^{3} + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.2.12

Raise $- 5$ to the power of $3$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 15 {(2 \sqrt[3]{x} - 5)}^{2} + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.3

Rewrite ${(2 \sqrt[3]{x} - 5)}^{2}$ as $(2 \sqrt[3]{x} - 5) (2 \sqrt[3]{x} - 5)$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 15 ((2 \sqrt[3]{x} - 5) (2 \sqrt[3]{x} - 5)) + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.4

Expand $(2 \sqrt[3]{x} - 5) (2 \sqrt[3]{x} - 5)$ using the FOIL Method.

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Step 5.2.4.4.1

Apply the distributive property.

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 15 (2 \sqrt[3]{x} (2 \sqrt[3]{x} - 5) - 5 (2 \sqrt[3]{x} - 5)) + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.4.2

Apply the distributive property.

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 15 (2 \sqrt[3]{x} (2 \sqrt[3]{x}) + 2 \sqrt[3]{x} \cdot - 5 - 5 (2 \sqrt[3]{x} - 5)) + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.4.3

Apply the distributive property.

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 15 (2 \sqrt[3]{x} (2 \sqrt[3]{x}) + 2 \sqrt[3]{x} \cdot - 5 - 5 (2 \sqrt[3]{x}) - 5 \cdot - 5) + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.5

Simplify and combine like terms.

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Step 5.2.4.5.1

Simplify each term.

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Step 5.2.4.5.1.1

Multiply $2 \sqrt[3]{x} (2 \sqrt[3]{x})$ .

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Step 5.2.4.5.1.1.1

Multiply $2$ by $2$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 15 (4 \sqrt[3]{x} \sqrt[3]{x} + 2 \sqrt[3]{x} \cdot - 5 - 5 (2 \sqrt[3]{x}) - 5 \cdot - 5) + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.5.1.1.2

Raise $\sqrt[3]{x}$ to the power of $1$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 15 (4 (\sqrt[3]{x} \sqrt[3]{x}) + 2 \sqrt[3]{x} \cdot - 5 - 5 (2 \sqrt[3]{x}) - 5 \cdot - 5) + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.5.1.1.3

Raise $\sqrt[3]{x}$ to the power of $1$ .

Step 5.2.4.5.1.1.4

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

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 15 (4 {\sqrt[3]{x}}^{1 + 1} + 2 \sqrt[3]{x} \cdot - 5 - 5 (2 \sqrt[3]{x}) - 5 \cdot - 5) + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.5.1.1.5

Add $1$ and $1$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 15 (4 {\sqrt[3]{x}}^{2} + 2 \sqrt[3]{x} \cdot - 5 - 5 (2 \sqrt[3]{x}) - 5 \cdot - 5) + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.5.1.2

Rewrite ${\sqrt[3]{x}}^{2}$ as $\sqrt[3]{x^{2}}$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 15 (4 \sqrt[3]{x^{2}} + 2 \sqrt[3]{x} \cdot - 5 - 5 (2 \sqrt[3]{x}) - 5 \cdot - 5) + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.5.1.3

Multiply $- 5$ by $2$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 15 (4 \sqrt[3]{x^{2}} - 10 \sqrt[3]{x} - 5 (2 \sqrt[3]{x}) - 5 \cdot - 5) + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.5.1.4

Multiply $2$ by $- 5$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 15 (4 \sqrt[3]{x^{2}} - 10 \sqrt[3]{x} - 10 \sqrt[3]{x} - 5 \cdot - 5) + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.5.1.5

Multiply $- 5$ by $- 5$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 15 (4 \sqrt[3]{x^{2}} - 10 \sqrt[3]{x} - 10 \sqrt[3]{x} + 25) + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.5.2

Subtract $10 \sqrt[3]{x}$ from $- 10 \sqrt[3]{x}$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 15 (4 \sqrt[3]{x^{2}} - 20 \sqrt[3]{x} + 25) + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.6

Apply the distributive property.

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 15 (4 \sqrt[3]{x^{2}}) + 15 (- 20 \sqrt[3]{x}) + 15 \cdot 25 + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.7

Simplify.

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Step 5.2.4.7.1

Multiply $4$ by $15$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 60 \sqrt[3]{x^{2}} + 15 (- 20 \sqrt[3]{x}) + 15 \cdot 25 + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.7.2

Multiply $- 20$ by $15$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 60 \sqrt[3]{x^{2}} - 300 \sqrt[3]{x} + 15 \cdot 25 + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.7.3

Multiply $15$ by $25$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 60 \sqrt[3]{x^{2}} - 300 \sqrt[3]{x} + 375 + 75 (2 \sqrt[3]{x} - 5) + 125}{8}$

Step 5.2.4.8

Apply the distributive property.

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 60 \sqrt[3]{x^{2}} - 300 \sqrt[3]{x} + 375 + 75 (2 \sqrt[3]{x}) + 75 \cdot - 5 + 125}{8}$

Step 5.2.4.9

Multiply $2$ by $75$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 60 \sqrt[3]{x^{2}} - 300 \sqrt[3]{x} + 375 + 150 \sqrt[3]{x} + 75 \cdot - 5 + 125}{8}$

Step 5.2.4.10

Multiply $75$ by $- 5$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 60 \sqrt[3]{x^{2}} - 300 \sqrt[3]{x} + 375 + 150 \sqrt[3]{x} - 375 + 125}{8}$

Step 5.2.5

Simplify terms.

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Step 5.2.5.1

Combine the opposite terms in $8 x - 60 \sqrt[3]{x^{2}} + 150 \sqrt[3]{x} - 125 + 60 \sqrt[3]{x^{2}} - 300 \sqrt[3]{x} + 375 + 150 \sqrt[3]{x} - 375 + 125$ .

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Step 5.2.5.1.1

Add $- 60 \sqrt[3]{x^{2}}$ and $60 \sqrt[3]{x^{2}}$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x + 0 + 150 \sqrt[3]{x} - 125 - 300 \sqrt[3]{x} + 375 + 150 \sqrt[3]{x} - 375 + 125}{8}$

Step 5.2.5.1.2

Add $8 x$ and $0$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x + 150 \sqrt[3]{x} - 125 - 300 \sqrt[3]{x} + 375 + 150 \sqrt[3]{x} - 375 + 125}{8}$

Step 5.2.5.1.3

Subtract $375$ from $375$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x + 150 \sqrt[3]{x} - 125 - 300 \sqrt[3]{x} + 0 + 150 \sqrt[3]{x} + 125}{8}$

Step 5.2.5.1.4

Add $8 x + 150 \sqrt[3]{x} - 125 - 300 \sqrt[3]{x}$ and $0$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x + 150 \sqrt[3]{x} - 125 - 300 \sqrt[3]{x} + 150 \sqrt[3]{x} + 125}{8}$

Step 5.2.5.1.5

Add $- 125$ and $125$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x + 150 \sqrt[3]{x} + 0 - 300 \sqrt[3]{x} + 150 \sqrt[3]{x}}{8}$

Step 5.2.5.1.6

Add $8 x + 150 \sqrt[3]{x}$ and $0$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x + 150 \sqrt[3]{x} - 300 \sqrt[3]{x} + 150 \sqrt[3]{x}}{8}$

Step 5.2.5.2

Subtract $300 \sqrt[3]{x}$ from $150 \sqrt[3]{x}$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x - 150 \sqrt[3]{x} + 150 \sqrt[3]{x}}{8}$

Step 5.2.5.3

Combine the opposite terms in $8 x - 150 \sqrt[3]{x} + 150 \sqrt[3]{x}$ .

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Step 5.2.5.3.1

Add $- 150 \sqrt[3]{x}$ and $150 \sqrt[3]{x}$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x + 0}{8}$

Step 5.2.5.3.2

Add $8 x$ and $0$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x}{8}$

Step 5.2.5.4

Cancel the common factor of $8$ .

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Step 5.2.5.4.1

Cancel the common factor.

$f^{- 1} (2 \sqrt[3]{x} - 5) = \frac{8 x}{8}$

Step 5.2.5.4.2

Divide $x$ by $1$ .

$f^{- 1} (2 \sqrt[3]{x} - 5) = x$

Step 5.3

Evaluate $f (f^{- 1} (x))$ .

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Step 5.3.1

Set up the composite result function.

$f (f^{- 1} (x))$

Step 5.3.2

Evaluate $f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8})$ by substituting in the value of $f^{- 1}$ into $f$ .

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = 2 \sqrt[3]{\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}} - 5$

Step 5.3.3

Remove parentheses.

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = 2 \sqrt[3]{\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}} - 5$

Step 5.3.4

Simplify each term.

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Step 5.3.4.1

Combine the numerators over the common denominator.

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = 2 \sqrt[3]{\frac{x^{3} + 15 x^{2} + 75 x + 125}{8}} - 5$

Step 5.3.4.2

Rewrite $\frac{x^{3} + 15 x^{2} + 75 x + 125}{8}$ as ${(\frac{1}{2})}^{3} (x^{3} + 15 x^{2} + 75 x + 125)$ .

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Step 5.3.4.2.1

Factor the perfect power $1^{3}$ out of $x^{3} + 15 x^{2} + 75 x + 125$ .

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = 2 \sqrt[3]{\frac{1^{3} (x^{3} + 15 x^{2} + 75 x + 125)}{8}} - 5$

Step 5.3.4.2.2

Factor the perfect power $2^{3}$ out of $8$ .

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = 2 \sqrt[3]{\frac{1^{3} (x^{3} + 15 x^{2} + 75 x + 125)}{2^{3} \cdot 1}} - 5$

Step 5.3.4.2.3

Rearrange the fraction $\frac{1^{3} (x^{3} + 15 x^{2} + 75 x + 125)}{2^{3} \cdot 1}$ .

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = 2 \sqrt[3]{{(\frac{1}{2})}^{3} (x^{3} + 15 x^{2} + 75 x + 125)} - 5$

Step 5.3.4.3

Pull terms out from under the radical.

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = 2 (\frac{1}{2} \cdot \sqrt[3]{x^{3} + 15 x^{2} + 75 x + 125}) - 5$

Step 5.3.4.4

Make each term match the terms from the binomial theorem formula.

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = 2 (\frac{1}{2} \cdot \sqrt[3]{x^{3} + 3 \cdot (5 x^{2}) + 3 \cdot (5^{2} x) + 5^{3}}) - 5$

Step 5.3.4.5

Factor $x^{3} + 3 \cdot 5 x^{2} + 3 \cdot 5^{2} x + 5^{3}$ using the binomial theorem.

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = 2 (\frac{1}{2} \cdot \sqrt[3]{{(x + 5)}^{3}}) - 5$

Step 5.3.4.6

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

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = 2 (\frac{1}{2} \cdot (x + 5)) - 5$

Step 5.3.4.7

Apply the distributive property.

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = 2 (\frac{1}{2} x + \frac{1}{2} \cdot 5) - 5$

Step 5.3.4.8

Combine $\frac{1}{2}$ and $x$ .

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = 2 (\frac{x}{2} + \frac{1}{2} \cdot 5) - 5$

Step 5.3.4.9

Combine $\frac{1}{2}$ and $5$ .

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = 2 (\frac{x}{2} + \frac{5}{2}) - 5$

Step 5.3.4.10

Apply the distributive property.

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = 2 (\frac{x}{2}) + 2 (\frac{5}{2}) - 5$

Step 5.3.4.11

Cancel the common factor of $2$ .

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Step 5.3.4.11.1

Cancel the common factor.

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = 2 (\frac{x}{2}) + 2 (\frac{5}{2}) - 5$

Step 5.3.4.11.2

Rewrite the expression.

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = x + 2 (\frac{5}{2}) - 5$

Step 5.3.4.12

Cancel the common factor of $2$ .

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Step 5.3.4.12.1

Cancel the common factor.

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = x + 2 (\frac{5}{2}) - 5$

Step 5.3.4.12.2

Rewrite the expression.

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = x + 5 - 5$

Step 5.3.5

Combine the opposite terms in $x + 5 - 5$ .

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Step 5.3.5.1

Subtract $5$ from $5$ .

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = x + 0$

Step 5.3.5.2

Add $x$ and $0$ .

$f (\frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}) = x$

Step 5.4

Since $f^{- 1} (f (x)) = x$ and $f (f^{- 1} (x)) = x$ , then $f^{- 1} (x) = \frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}$ is the inverse of $f (x) = 2 \sqrt[3]{x} - 5$ .

$f^{- 1} (x) = \frac{x^{3}}{8} + \frac{15 x^{2}}{8} + \frac{75 x}{8} + \frac{125}{8}$