Find the Inverse f(x)=8x+4

$f (x) = 8 x + 4$

Step 1

Write $f (x) = 8 x + 4$ as an equation.

$y = 8 x + 4$

Step 2

Interchange the variables.

$x = 8 y + 4$

Step 3

Solve for $y$ .

Rewrite the equation as $8 y + 4 = x$ .

$8 y + 4 = x$

Subtract $4$ from both sides of the equation.

$8 y = x - 4$

Divide each term in $8 y = x - 4$ by $8$ and simplify.

Divide each term in $8 y = x - 4$ by $8$ .

$\frac{8 y}{8} = \frac{x}{8} + \frac{- 4}{8}$

Simplify the left side.

Cancel the common factor of $8$ .

Cancel the common factor.

$\frac{8 y}{8} = \frac{x}{8} + \frac{- 4}{8}$

Divide $y$ by $1$ .

$y = \frac{x}{8} + \frac{- 4}{8}$

Simplify the right side.

Simplify each term.

Cancel the common factor of $- 4$ and $8$ .

Factor $4$ out of $- 4$ .

$y = \frac{x}{8} + \frac{4 (- 1)}{8}$

Cancel the common factors.

Factor $4$ out of $8$ .

$y = \frac{x}{8} + \frac{4 \cdot - 1}{4 \cdot 2}$

Cancel the common factor.

$y = \frac{x}{8} + \frac{4 \cdot - 1}{4 \cdot 2}$

Rewrite the expression.

$y = \frac{x}{8} + \frac{- 1}{2}$

Move the negative in front of the fraction.

$y = \frac{x}{8} - \frac{1}{2}$

Step 4

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

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

Step 5

Verify if $f^{- 1} (x) = \frac{x}{8} - \frac{1}{2}$ is the inverse of $f (x) = 8 x + 4$ .

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

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

Set up the composite result function.

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

Evaluate $f^{- 1} (8 x + 4)$ by substituting in the value of $f$ into $f^{- 1}$ .

$f^{- 1} (8 x + 4) = \frac{8 x + 4}{8} - \frac{1}{2}$

Cancel the common factor of $8 x + 4$ and $8$ .

Factor $4$ out of $8 x$ .

$f^{- 1} (8 x + 4) = \frac{4 (2 x) + 4}{8} - \frac{1}{2}$

Factor $4$ out of $4$ .

$f^{- 1} (8 x + 4) = \frac{4 (2 x) + 4 (1)}{8} - \frac{1}{2}$

Factor $4$ out of $4 (2 x) + 4 (1)$ .

$f^{- 1} (8 x + 4) = \frac{4 (2 x + 1)}{8} - \frac{1}{2}$

Cancel the common factors.

Factor $4$ out of $8$ .

$f^{- 1} (8 x + 4) = \frac{4 (2 x + 1)}{4 (2)} - \frac{1}{2}$

Cancel the common factor.

$f^{- 1} (8 x + 4) = \frac{4 (2 x + 1)}{4 \cdot 2} - \frac{1}{2}$

Rewrite the expression.

$f^{- 1} (8 x + 4) = \frac{2 x + 1}{2} - \frac{1}{2}$

Combine the numerators over the common denominator.

$f^{- 1} (8 x + 4) = \frac{2 x + 1 - 1}{2}$

Combine the opposite terms in $2 x + 1 - 1$ .

Subtract $1$ from $1$ .

$f^{- 1} (8 x + 4) = \frac{2 x + 0}{2}$

Add $2 x$ and $0$ .

$f^{- 1} (8 x + 4) = \frac{2 x}{2}$

Cancel the common factor of $2$ .

Cancel the common factor.

$f^{- 1} (8 x + 4) = \frac{2 x}{2}$

Divide $x$ by $1$ .

$f^{- 1} (8 x + 4) = x$

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

Set up the composite result function.

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

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

$f (\frac{x}{8} - \frac{1}{2}) = 8 (\frac{x}{8} - \frac{1}{2}) + 4$

Simplify each term.

Apply the distributive property.

$f (\frac{x}{8} - \frac{1}{2}) = 8 (\frac{x}{8}) + 8 (- \frac{1}{2}) + 4$

Cancel the common factor of $8$ .

Cancel the common factor.

$f (\frac{x}{8} - \frac{1}{2}) = 8 (\frac{x}{8}) + 8 (- \frac{1}{2}) + 4$

Rewrite the expression.

$f (\frac{x}{8} - \frac{1}{2}) = x + 8 (- \frac{1}{2}) + 4$

Cancel the common factor of $2$ .

Move the leading negative in $- \frac{1}{2}$ into the numerator.

$f (\frac{x}{8} - \frac{1}{2}) = x + 8 (\frac{- 1}{2}) + 4$

Factor $2$ out of $8$ .

$f (\frac{x}{8} - \frac{1}{2}) = x + 2 (4) (\frac{- 1}{2}) + 4$

Cancel the common factor.

$f (\frac{x}{8} - \frac{1}{2}) = x + 2 \cdot (4 (\frac{- 1}{2})) + 4$

Rewrite the expression.

$f (\frac{x}{8} - \frac{1}{2}) = x + 4 \cdot - 1 + 4$

Multiply $4$ by $- 1$ .

$f (\frac{x}{8} - \frac{1}{2}) = x - 4 + 4$

Combine the opposite terms in $x - 4 + 4$ .

Add $- 4$ and $4$ .

$f (\frac{x}{8} - \frac{1}{2}) = x + 0$

Add $x$ and $0$ .

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

Since $f^{- 1} (f (x)) = x$ and $f (f^{- 1} (x)) = x$ , then $f^{- 1} (x) = \frac{x}{8} - \frac{1}{2}$ is the inverse of $f (x) = 8 x + 4$ .

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

Find the Inverse f(x)=8x+4

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