Precalculus Examples

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

Step 1

Consider the difference quotient formula.

$\frac{f (x + h) - f (x)}{h}$

Step 2

Find the components of the definition.

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Step 2.1

Evaluate the function at $x = x + h$ .

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Step 2.1.1

Replace the variable $x$ with $x + h$ in the expression.

$f (x + h) = \frac{1}{8} \cdot {(x + h)}^{3} - {(x + h)}^{2}$

Step 2.1.2

Simplify the result.

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Step 2.1.2.1

Simplify each term.

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Step 2.1.2.1.1

Use the Binomial Theorem.

$f (x + h) = \frac{1}{8} \cdot (x^{3} + 3 x^{2} h + 3 x h^{2} + h^{3}) - {(x + h)}^{2}$

Step 2.1.2.1.2

Apply the distributive property.

$f (x + h) = \frac{1}{8} x^{3} + \frac{1}{8} \cdot (3 x^{2} h) + \frac{1}{8} \cdot (3 x h^{2}) + \frac{1}{8} h^{3} - {(x + h)}^{2}$

Step 2.1.2.1.3

Simplify.

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Step 2.1.2.1.3.1

Combine $\frac{1}{8}$ and $x^{3}$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{1}{8} \cdot (3 x^{2} h) + \frac{1}{8} \cdot (3 x h^{2}) + \frac{1}{8} h^{3} - {(x + h)}^{2}$

Step 2.1.2.1.3.2

Multiply $\frac{1}{8} (3 x^{2} h)$ .

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Step 2.1.2.1.3.2.1

Combine $3$ and $\frac{1}{8}$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{3}{8} \cdot (x^{2} h) + \frac{1}{8} \cdot (3 x h^{2}) + \frac{1}{8} h^{3} - {(x + h)}^{2}$

Step 2.1.2.1.3.2.2

Combine $x^{2}$ and $\frac{3}{8}$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{x^{2} \cdot 3}{8} \cdot h + \frac{1}{8} \cdot (3 x h^{2}) + \frac{1}{8} h^{3} - {(x + h)}^{2}$

Step 2.1.2.1.3.2.3

Combine $\frac{x^{2} \cdot 3}{8}$ and $h$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{x^{2} \cdot (3 h)}{8} + \frac{1}{8} \cdot (3 x h^{2}) + \frac{1}{8} h^{3} - {(x + h)}^{2}$

Step 2.1.2.1.3.3

Multiply $\frac{1}{8} (3 x h^{2})$ .

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Step 2.1.2.1.3.3.1

Combine $3$ and $\frac{1}{8}$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{x^{2} \cdot (3 h)}{8} + \frac{3}{8} \cdot (x h^{2}) + \frac{1}{8} h^{3} - {(x + h)}^{2}$

Step 2.1.2.1.3.3.2

Combine $x$ and $\frac{3}{8}$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{x^{2} \cdot (3 h)}{8} + \frac{x \cdot 3}{8} \cdot h^{2} + \frac{1}{8} h^{3} - {(x + h)}^{2}$

Step 2.1.2.1.3.3.3

Combine $\frac{x \cdot 3}{8}$ and $h^{2}$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{x^{2} \cdot (3 h)}{8} + \frac{x \cdot (3 h^{2})}{8} + \frac{1}{8} h^{3} - {(x + h)}^{2}$

Step 2.1.2.1.3.4

Combine $\frac{1}{8}$ and $h^{3}$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{x^{2} \cdot (3 h)}{8} + \frac{x \cdot (3 h^{2})}{8} + \frac{h^{3}}{8} - {(x + h)}^{2}$

Step 2.1.2.1.4

Simplify each term.

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Step 2.1.2.1.4.1

Move $3$ to the left of $x^{2}$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{3 \cdot (x^{2} h)}{8} + \frac{x \cdot (3 h^{2})}{8} + \frac{h^{3}}{8} - {(x + h)}^{2}$

Step 2.1.2.1.4.2

Move $3$ to the left of $x$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{3 x^{2} h}{8} + \frac{3 x h^{2}}{8} + \frac{h^{3}}{8} - {(x + h)}^{2}$

Step 2.1.2.1.5

Rewrite ${(x + h)}^{2}$ as $(x + h) (x + h)$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{3 x^{2} h}{8} + \frac{3 x h^{2}}{8} + \frac{h^{3}}{8} - ((x + h) (x + h))$

Step 2.1.2.1.6

Expand $(x + h) (x + h)$ using the FOIL Method.

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Step 2.1.2.1.6.1

Apply the distributive property.

$f (x + h) = \frac{x^{3}}{8} + \frac{3 x^{2} h}{8} + \frac{3 x h^{2}}{8} + \frac{h^{3}}{8} - (x (x + h) + h (x + h))$

Step 2.1.2.1.6.2

Apply the distributive property.

$f (x + h) = \frac{x^{3}}{8} + \frac{3 x^{2} h}{8} + \frac{3 x h^{2}}{8} + \frac{h^{3}}{8} - (x \cdot x + x h + h (x + h))$

Step 2.1.2.1.6.3

Apply the distributive property.

$f (x + h) = \frac{x^{3}}{8} + \frac{3 x^{2} h}{8} + \frac{3 x h^{2}}{8} + \frac{h^{3}}{8} - (x \cdot x + x h + h x + h \cdot h)$

Step 2.1.2.1.7

Simplify and combine like terms.

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Step 2.1.2.1.7.1

Simplify each term.

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Step 2.1.2.1.7.1.1

Multiply $x$ by $x$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{3 x^{2} h}{8} + \frac{3 x h^{2}}{8} + \frac{h^{3}}{8} - (x^{2} + x h + h x + h \cdot h)$

Step 2.1.2.1.7.1.2

Multiply $h$ by $h$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{3 x^{2} h}{8} + \frac{3 x h^{2}}{8} + \frac{h^{3}}{8} - (x^{2} + x h + h x + h^{2})$

Step 2.1.2.1.7.2

Add $x h$ and $h x$ .

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Step 2.1.2.1.7.2.1

Reorder $x$ and $h$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{3 x^{2} h}{8} + \frac{3 x h^{2}}{8} + \frac{h^{3}}{8} - (x^{2} + h x + h x + h^{2})$

Step 2.1.2.1.7.2.2

Add $h x$ and $h x$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{3 x^{2} h}{8} + \frac{3 x h^{2}}{8} + \frac{h^{3}}{8} - (x^{2} + 2 h x + h^{2})$

Step 2.1.2.1.8

Apply the distributive property.

$f (x + h) = \frac{x^{3}}{8} + \frac{3 x^{2} h}{8} + \frac{3 x h^{2}}{8} + \frac{h^{3}}{8} - x^{2} - (2 h x) - h^{2}$

Step 2.1.2.1.9

Multiply $2$ by $- 1$ .

$f (x + h) = \frac{x^{3}}{8} + \frac{3 x^{2} h}{8} + \frac{3 x h^{2}}{8} + \frac{h^{3}}{8} - x^{2} - 2 h x - h^{2}$

Step 2.1.2.2

The final answer is $\frac{x^{3}}{8} + \frac{3 x^{2} h}{8} + \frac{3 x h^{2}}{8} + \frac{h^{3}}{8} - x^{2} - 2 h x - h^{2}$ .

$\frac{x^{3}}{8} + \frac{3 x^{2} h}{8} + \frac{3 x h^{2}}{8} + \frac{h^{3}}{8} - x^{2} - 2 h x - h^{2}$

Step 2.2

Reorder.

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Step 2.2.1

Move $x^{2}$ .

$\frac{x^{3}}{8} + \frac{3 h x^{2}}{8} + \frac{3 x h^{2}}{8} + \frac{h^{3}}{8} - x^{2} - 2 h x - h^{2}$

Step 2.2.2

Move $x$ .

$\frac{x^{3}}{8} + \frac{3 h x^{2}}{8} + \frac{3 h^{2} x}{8} + \frac{h^{3}}{8} - x^{2} - 2 h x - h^{2}$

Step 2.2.3

Move $- x^{2}$ .

$\frac{x^{3}}{8} + \frac{3 h x^{2}}{8} + \frac{3 h^{2} x}{8} + \frac{h^{3}}{8} - 2 h x - h^{2} - x^{2}$

Step 2.2.4

Move $- 2 h x$ .

$\frac{x^{3}}{8} + \frac{3 h x^{2}}{8} + \frac{3 h^{2} x}{8} + \frac{h^{3}}{8} - h^{2} - 2 h x - x^{2}$

Step 2.2.5

Move $\frac{x^{3}}{8}$ .

$\frac{3 h x^{2}}{8} + \frac{3 h^{2} x}{8} + \frac{h^{3}}{8} + \frac{x^{3}}{8} - h^{2} - 2 h x - x^{2}$

Step 2.2.6

Move $\frac{3 h x^{2}}{8}$ .

$\frac{3 h^{2} x}{8} + \frac{h^{3}}{8} + \frac{3 h x^{2}}{8} + \frac{x^{3}}{8} - h^{2} - 2 h x - x^{2}$

Step 2.2.7

Reorder $\frac{3 h^{2} x}{8}$ and $\frac{h^{3}}{8}$ .

$\frac{h^{3}}{8} + \frac{3 h^{2} x}{8} + \frac{3 h x^{2}}{8} + \frac{x^{3}}{8} - h^{2} - 2 h x - x^{2}$

Step 2.3

Find the components of the definition.

$f (x + h) = \frac{h^{3}}{8} + \frac{3 h^{2} x}{8} + \frac{3 h x^{2}}{8} + \frac{x^{3}}{8} - h^{2} - 2 h x - x^{2}$

$f (x) = \frac{x^{3}}{8} - x^{2}$

$f (x + h) = \frac{h^{3}}{8} + \frac{3 h^{2} x}{8} + \frac{3 h x^{2}}{8} + \frac{x^{3}}{8} - h^{2} - 2 h x - x^{2}$

$f (x) = \frac{x^{3}}{8} - x^{2}$

Step 3

Plug in the components.

$\frac{f (x + h) - f (x)}{h} = \frac{\frac{h^{3}}{8} + \frac{3 h^{2} x}{8} + \frac{3 h x^{2}}{8} + \frac{x^{3}}{8} - h^{2} - 2 h x - x^{2} - (\frac{x^{3}}{8} - x^{2})}{h}$

Step 4

Simplify.

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Step 4.1

Simplify the numerator.

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Step 4.1.1

Apply the distributive property.

$\frac{\frac{h^{3}}{8} + \frac{3 h^{2} x}{8} + \frac{3 h x^{2}}{8} + \frac{x^{3}}{8} - h^{2} - 2 h x - x^{2} - \frac{x^{3}}{8} - - x^{2}}{h}$

Step 4.1.2

Multiply $- - x^{2}$ .

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Step 4.1.2.1

Multiply $- 1$ by $- 1$ .

$\frac{\frac{h^{3}}{8} + \frac{3 h^{2} x}{8} + \frac{3 h x^{2}}{8} + \frac{x^{3}}{8} - h^{2} - 2 h x - x^{2} - \frac{x^{3}}{8} + 1 x^{2}}{h}$

Step 4.1.2.2

Multiply $x^{2}$ by $1$ .

$\frac{\frac{h^{3}}{8} + \frac{3 h^{2} x}{8} + \frac{3 h x^{2}}{8} + \frac{x^{3}}{8} - h^{2} - 2 h x - x^{2} - \frac{x^{3}}{8} + x^{2}}{h}$

Step 4.1.3

Subtract $\frac{x^{3}}{8}$ from $\frac{x^{3}}{8}$ .

$\frac{\frac{h^{3}}{8} + \frac{3 h^{2} x}{8} + \frac{3 h x^{2}}{8} - h^{2} - 2 h x - x^{2} + 0 + x^{2}}{h}$

Step 4.1.4

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

$\frac{\frac{h^{3}}{8} + \frac{3 h^{2} x}{8} + \frac{3 h x^{2}}{8} - h^{2} - 2 h x - x^{2} + x^{2}}{h}$

Step 4.1.5

Add $- x^{2}$ and $x^{2}$ .

$\frac{\frac{h^{3}}{8} + \frac{3 h^{2} x}{8} + \frac{3 h x^{2}}{8} - h^{2} - 2 h x + 0}{h}$

Step 4.1.6

Add $\frac{h^{3}}{8} + \frac{3 h^{2} x}{8} + \frac{3 h x^{2}}{8} - h^{2} - 2 h x$ and $0$ .

$\frac{\frac{h^{3}}{8} + \frac{3 h^{2} x}{8} + \frac{3 h x^{2}}{8} - h^{2} - 2 h x}{h}$

Step 4.1.7

Combine the numerators over the common denominator.

$\frac{\frac{h^{3} + 3 h^{2} x}{8} + \frac{3 h x^{2}}{8} - h^{2} - 2 h x}{h}$

Step 4.1.8

Factor $h^{2}$ out of $h^{3} + 3 h^{2} x$ .

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Step 4.1.8.1

Factor $h^{2}$ out of $h^{3}$ .

$\frac{\frac{h^{2} h + 3 h^{2} x}{8} + \frac{3 h x^{2}}{8} - h^{2} - 2 h x}{h}$

Step 4.1.8.2

Factor $h^{2}$ out of $3 h^{2} x$ .

$\frac{\frac{h^{2} h + h^{2} (3 x)}{8} + \frac{3 h x^{2}}{8} - h^{2} - 2 h x}{h}$

Step 4.1.8.3

Factor $h^{2}$ out of $h^{2} h + h^{2} (3 x)$ .

$\frac{\frac{h^{2} (h + 3 x)}{8} + \frac{3 h x^{2}}{8} - h^{2} - 2 h x}{h}$

Step 4.1.9

Combine the numerators over the common denominator.

$\frac{\frac{h^{2} (h + 3 x) + 3 h x^{2}}{8} - h^{2} - 2 h x}{h}$

Step 4.1.10

Simplify the numerator.

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Step 4.1.10.1

Factor $h$ out of $h^{2} (h + 3 x) + 3 h x^{2}$ .

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Step 4.1.10.1.1

Factor $h$ out of $h^{2} (h + 3 x)$ .

$\frac{\frac{h (h (h + 3 x)) + 3 h x^{2}}{8} - h^{2} - 2 h x}{h}$

Step 4.1.10.1.2

Factor $h$ out of $3 h x^{2}$ .

$\frac{\frac{h (h (h + 3 x)) + h (3 x^{2})}{8} - h^{2} - 2 h x}{h}$

Step 4.1.10.1.3

Factor $h$ out of $h (h (h + 3 x)) + h (3 x^{2})$ .

$\frac{\frac{h (h (h + 3 x) + 3 x^{2})}{8} - h^{2} - 2 h x}{h}$

Step 4.1.10.2

Apply the distributive property.

$\frac{\frac{h (h (h) + h (3 x) + 3 x^{2})}{8} - h^{2} - 2 h x}{h}$

Step 4.1.10.3

Multiply $h$ by $h$ .

$\frac{\frac{h (h^{2} + h (3 x) + 3 x^{2})}{8} - h^{2} - 2 h x}{h}$

Step 4.1.10.4

Rewrite using the commutative property of multiplication.

$\frac{\frac{h (h^{2} + 3 h x + 3 x^{2})}{8} - h^{2} - 2 h x}{h}$

Step 4.1.11

To write $- h^{2}$ as a fraction with a common denominator, multiply by $\frac{8}{8}$ .

$\frac{\frac{h (h^{2} + 3 h x + 3 x^{2})}{8} - h^{2} \cdot \frac{8}{8} - 2 h x}{h}$

Step 4.1.12

Combine $- h^{2}$ and $\frac{8}{8}$ .

$\frac{\frac{h (h^{2} + 3 h x + 3 x^{2})}{8} + \frac{- h^{2} \cdot 8}{8} - 2 h x}{h}$

Step 4.1.13

Combine the numerators over the common denominator.

$\frac{\frac{h (h^{2} + 3 h x + 3 x^{2}) - h^{2} \cdot 8}{8} - 2 h x}{h}$

Step 4.1.14

Simplify the numerator.

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Step 4.1.14.1

Factor $h$ out of $h (h^{2} + 3 h x + 3 x^{2}) - h^{2} \cdot 8$ .

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Step 4.1.14.1.1

Factor $h$ out of $- h^{2} \cdot 8$ .

$\frac{\frac{h (h^{2} + 3 h x + 3 x^{2}) + h (- h \cdot 8)}{8} - 2 h x}{h}$

Step 4.1.14.1.2

Factor $h$ out of $h (h^{2} + 3 h x + 3 x^{2}) + h (- h \cdot 8)$ .

$\frac{\frac{h (h^{2} + 3 h x + 3 x^{2} - h \cdot 8)}{8} - 2 h x}{h}$

Step 4.1.14.2

Multiply $8$ by $- 1$ .

$\frac{\frac{h (h^{2} + 3 h x + 3 x^{2} - 8 h)}{8} - 2 h x}{h}$

Step 4.1.15

To write $- 2 h x$ as a fraction with a common denominator, multiply by $\frac{8}{8}$ .

$\frac{\frac{h (h^{2} + 3 h x + 3 x^{2} - 8 h)}{8} - 2 h x \cdot \frac{8}{8}}{h}$

Step 4.1.16

Combine $- 2 h x$ and $\frac{8}{8}$ .

$\frac{\frac{h (h^{2} + 3 h x + 3 x^{2} - 8 h)}{8} + \frac{- 2 h x \cdot 8}{8}}{h}$

Step 4.1.17

Combine the numerators over the common denominator.

$\frac{\frac{h (h^{2} + 3 h x + 3 x^{2} - 8 h) - 2 h x \cdot 8}{8}}{h}$

Step 4.1.18

Simplify the numerator.

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Step 4.1.18.1

Factor $h$ out of $h (h^{2} + 3 h x + 3 x^{2} - 8 h) - 2 h x \cdot 8$ .

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Step 4.1.18.1.1

Factor $h$ out of $- 2 h x \cdot 8$ .

$\frac{\frac{h (h^{2} + 3 h x + 3 x^{2} - 8 h) + h (- 2 x \cdot 8)}{8}}{h}$

Step 4.1.18.1.2

Factor $h$ out of $h (h^{2} + 3 h x + 3 x^{2} - 8 h) + h (- 2 x \cdot 8)$ .

$\frac{\frac{h (h^{2} + 3 h x + 3 x^{2} - 8 h - 2 x \cdot 8)}{8}}{h}$

Step 4.1.18.2

Multiply $8$ by $- 2$ .

$\frac{\frac{h (h^{2} + 3 h x + 3 x^{2} - 8 h - 16 x)}{8}}{h}$

Step 4.2

Multiply the numerator by the reciprocal of the denominator.

$\frac{h (h^{2} + 3 h x + 3 x^{2} - 8 h - 16 x)}{8} \cdot \frac{1}{h}$

Step 4.3

Combine.

$\frac{h (h^{2} + 3 h x + 3 x^{2} - 8 h - 16 x) \cdot 1}{8 h}$

Step 4.4

Cancel the common factor of $h$ .

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Step 4.4.1

Cancel the common factor.

$\frac{h (h^{2} + 3 h x + 3 x^{2} - 8 h - 16 x) \cdot 1}{8 h}$

Step 4.4.2

Rewrite the expression.

$\frac{(h^{2} + 3 h x + 3 x^{2} - 8 h - 16 x) \cdot 1}{8}$

Step 4.5

Multiply $h^{2} + 3 h x + 3 x^{2} - 8 h - 16 x$ by $1$ .

$\frac{h^{2} + 3 h x + 3 x^{2} - 8 h - 16 x}{8}$

Step 5