Precalculus Examples

$f (x) = \frac{5 x + 4}{x + 6}$ , $g (x) = \frac{6 x - 4}{5 - x}$

Step 1

Set up the composite result function.

$f (g (x))$

Step 2

Evaluate $f (\frac{6 x - 4}{5 - x})$ by substituting in the value of $g$ into $f$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{5 (\frac{6 x - 4}{5 - x}) + 4}{(\frac{6 x - 4}{5 - x}) + 6}$

Step 3

Multiply the numerator and denominator of the fraction by $5 - x$ .

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Step 3.1

Multiply $\frac{5 \frac{6 x - 4}{5 - x} + 4}{\frac{6 x - 4}{5 - x} + 6}$ by $\frac{5 - x}{5 - x}$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{5 - x}{5 - x} \cdot \frac{5 (\frac{6 x - 4}{5 - x}) + 4}{\frac{6 x - 4}{5 - x} + 6}$

Step 3.2

Combine.

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (5 (\frac{6 x - 4}{5 - x}) + 4)}{(5 - x) (\frac{6 x - 4}{5 - x} + 6)}$

Step 4

Apply the distributive property.

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (5 (\frac{6 x - 4}{5 - x})) + (5 - x) \cdot 4}{(5 - x) (\frac{6 x - 4}{5 - x}) + (5 - x) \cdot 6}$

Step 5

Simplify with factoring out.

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Step 5.1

Factor $2$ out of $6 x - 4$ .

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Step 5.1.1

Factor $2$ out of $6 x$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (5 (\frac{6 x - 4}{5 - x})) + (5 - x) \cdot 4}{(5 - x) (\frac{2 (3 x) - 4}{5 - x}) + (5 - x) \cdot 6}$

Step 5.1.2

Factor $2$ out of $- 4$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (5 (\frac{6 x - 4}{5 - x})) + (5 - x) \cdot 4}{(5 - x) (\frac{2 (3 x) + 2 (- 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 5.1.3

Factor $2$ out of $2 (3 x) + 2 (- 2)$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (5 (\frac{6 x - 4}{5 - x})) + (5 - x) \cdot 4}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 5.2

Factor $2$ out of $6 x - 4$ .

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Step 5.2.1

Factor $2$ out of $6 x$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) \cdot (5 (\frac{2 (3 x) - 4}{5 - x})) + (5 - x) \cdot 4}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 5.2.2

Factor $2$ out of $- 4$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) \cdot (5 (\frac{2 (3 x) + 2 (- 2)}{5 - x})) + (5 - x) \cdot 4}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 5.2.3

Factor $2$ out of $2 (3 x) + 2 (- 2)$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) \cdot (5 (\frac{2 (3 x - 2)}{5 - x})) + (5 - x) \cdot 4}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6

Simplify the numerator.

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Step 6.1

Factor $5 - x$ out of $(5 - x) \cdot 5 \frac{2 (3 x - 2)}{5 - x} + (5 - x) \cdot 4$ .

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Step 6.1.1

Factor $5 - x$ out of $(5 - x) \cdot 5 \frac{2 (3 x - 2)}{5 - x}$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (5 (\frac{2 (3 x - 2)}{5 - x})) + (5 - x) \cdot 4}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.1.2

Factor $5 - x$ out of $(5 - x) \cdot 4$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (5 (\frac{2 (3 x - 2)}{5 - x})) + (5 - x) (4)}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.1.3

Factor $5 - x$ out of $(5 - x) (5 \frac{2 (3 x - 2)}{5 - x}) + (5 - x) (4)$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (5 (\frac{2 (3 x - 2)}{5 - x}) + 4)}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.2

Multiply $5 \frac{2 (3 x - 2)}{5 - x}$ .

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Step 6.2.1

Combine $5$ and $\frac{2 (3 x - 2)}{5 - x}$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{5 (2 (3 x - 2))}{5 - x} + 4)}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.2.2

Multiply $2$ by $5$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{10 (3 x - 2)}{5 - x} + 4)}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.3

To write $4$ as a fraction with a common denominator, multiply by $\frac{5 - x}{5 - x}$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{10 (3 x - 2)}{5 - x} + \frac{4 (5 - x)}{5 - x})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.4

Combine the numerators over the common denominator.

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{10 (3 x - 2) + 4 (5 - x)}{5 - x})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.5

Reorder terms.

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{10 (3 x - 2) + 4 (5 - x)}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.6

Rewrite $\frac{10 (3 x - 2) + 4 (5 - x)}{- x + 5}$ in a factored form.

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Step 6.6.1

Factor $2$ out of $10 (3 x - 2) + 4 (5 - x)$ .

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Step 6.6.1.1

Factor $2$ out of $10 (3 x - 2)$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{2 (5 (3 x - 2)) + 4 (5 - x)}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.6.1.2

Factor $2$ out of $4 (5 - x)$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{2 (5 (3 x - 2)) + 2 (2 (5 - x))}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.6.1.3

Factor $2$ out of $2 (5 (3 x - 2)) + 2 (2 (5 - x))$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{2 (5 (3 x - 2) + 2 (5 - x))}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.6.2

Apply the distributive property.

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{2 (5 (3 x) + 5 \cdot - 2 + 2 (5 - x))}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.6.3

Multiply $3$ by $5$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{2 (15 x + 5 \cdot - 2 + 2 (5 - x))}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.6.4

Multiply $5$ by $- 2$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{2 (15 x - 10 + 2 (5 - x))}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.6.5

Apply the distributive property.

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{2 (15 x - 10 + 2 \cdot 5 + 2 (- x))}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.6.6

Multiply $2$ by $5$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{2 (15 x - 10 + 10 + 2 (- x))}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.6.7

Multiply $- 1$ by $2$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{2 (15 x - 10 + 10 - 2 x)}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.6.8

Subtract $2 x$ from $15 x$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{2 (13 x - 10 + 10)}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.6.9

Add $- 10$ and $10$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{2 (13 x + 0)}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.6.10

Add $13 x$ and $0$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{2 \cdot (13 x)}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 6.6.11

Multiply $2$ by $13$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 7

Simplify the denominator.

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Step 7.1

Factor $5 - x$ out of $(5 - x) \frac{2 (3 x - 2)}{5 - x} + (5 - x) \cdot 6$ .

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Step 7.1.1

Factor $5 - x$ out of $(5 - x) \frac{2 (3 x - 2)}{5 - x}$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) \cdot 6}$

Step 7.1.2

Factor $5 - x$ out of $(5 - x) \cdot 6$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) (6)}$

Step 7.1.3

Factor $5 - x$ out of $(5 - x) (\frac{2 (3 x - 2)}{5 - x}) + (5 - x) (6)$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x} + 6)}$

Step 7.2

To write $6$ as a fraction with a common denominator, multiply by $\frac{5 - x}{5 - x}$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2)}{5 - x} + \frac{6 (5 - x)}{5 - x})}$

Step 7.3

Combine the numerators over the common denominator.

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2) + 6 (5 - x)}{5 - x})}$

Step 7.4

Rewrite $\frac{2 (3 x - 2) + 6 (5 - x)}{5 - x}$ in a factored form.

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Step 7.4.1

Factor $2$ out of $2 (3 x - 2) + 6 (5 - x)$ .

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Step 7.4.1.1

Factor $2$ out of $6 (5 - x)$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2) + 2 (3 (5 - x))}{5 - x})}$

Step 7.4.1.2

Factor $2$ out of $2 (3 x - 2) + 2 (3 (5 - x))$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2 + 3 (5 - x))}{5 - x})}$

Step 7.4.2

Apply the distributive property.

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2 + 3 \cdot 5 + 3 (- x))}{5 - x})}$

Step 7.4.3

Multiply $3$ by $5$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2 + 15 + 3 (- x))}{5 - x})}$

Step 7.4.4

Multiply $- 1$ by $3$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{2 (3 x - 2 + 15 - 3 x)}{5 - x})}$

Step 7.4.5

Subtract $3 x$ from $3 x$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{2 (0 - 2 + 15)}{5 - x})}$

Step 7.4.6

Subtract $2$ from $0$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{2 (- 2 + 15)}{5 - x})}$

Step 7.4.7

Add $- 2$ and $15$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{2 \cdot 13}{5 - x})}$

Step 7.5

Multiply $2$ by $13$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{26}{5 - x})}$

Step 8

Cancel the common factor of $5 - x$ .

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Step 8.1

Cancel the common factor.

$f (\frac{6 x - 4}{5 - x}) = \frac{(5 - x) (\frac{26 x}{- x + 5})}{(5 - x) (\frac{26}{5 - x})}$

Step 8.2

Rewrite the expression.

$f (\frac{6 x - 4}{5 - x}) = \frac{\frac{26 x}{- x + 5}}{\frac{26}{5 - x}}$

Step 9

Multiply the numerator by the reciprocal of the denominator.

$f (\frac{6 x - 4}{5 - x}) = \frac{26 x}{- x + 5} \cdot \frac{5 - x}{26}$

Step 10

Cancel the common factor of $26$ .

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Step 10.1

Factor $26$ out of $26 x$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{26 (x)}{- x + 5} \cdot \frac{5 - x}{26}$

Step 10.2

Cancel the common factor.

$f (\frac{6 x - 4}{5 - x}) = \frac{26 x}{- x + 5} \cdot \frac{5 - x}{26}$

Step 10.3

Rewrite the expression.

$f (\frac{6 x - 4}{5 - x}) = \frac{x}{- x + 5} \cdot (5 - x)$

Step 11

Multiply $\frac{x}{- x + 5}$ by $5 - x$ .

$f (\frac{6 x - 4}{5 - x}) = \frac{x (5 - x)}{- x + 5}$

Step 12

Cancel the common factor of $5 - x$ and $- x + 5$ .

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Step 12.1

Reorder terms.

$f (\frac{6 x - 4}{5 - x}) = \frac{x (- x + 5)}{- x + 5}$

Step 12.2

Cancel the common factor.

$f (\frac{6 x - 4}{5 - x}) = \frac{x (- x + 5)}{- x + 5}$

Step 12.3

Divide $x$ by $1$ .

$f (\frac{6 x - 4}{5 - x}) = x$