Find the Inverse f(x)=9x+4

$f (x) = 9 x + 4$

Step 1

Write $f (x) = 9 x + 4$ as an equation.

$y = 9 x + 4$

Step 2

Interchange the variables.

$x = 9 y + 4$

Step 3

Solve for $y$ .

Rewrite the equation as $9 y + 4 = x$ .

$9 y + 4 = x$

Subtract $4$ from both sides of the equation.

$9 y = x - 4$

Divide each term in $9 y = x - 4$ by $9$ and simplify.

Divide each term in $9 y = x - 4$ by $9$ .

$\frac{9 y}{9} = \frac{x}{9} + \frac{- 4}{9}$

Simplify the left side.

Cancel the common factor of $9$ .

Cancel the common factor.

$\frac{9 y}{9} = \frac{x}{9} + \frac{- 4}{9}$

Divide $y$ by $1$ .

$y = \frac{x}{9} + \frac{- 4}{9}$

Simplify the right side.

Move the negative in front of the fraction.

$y = \frac{x}{9} - \frac{4}{9}$

Step 4

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

$f^{- 1} (x) = \frac{x}{9} - \frac{4}{9}$

Step 5

Verify if $f^{- 1} (x) = \frac{x}{9} - \frac{4}{9}$ is the inverse of $f (x) = 9 x + 4$ .

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 $f^{- 1} (9 x + 4)$ by substituting in the value of $f$ into $f^{- 1}$ .

$f^{- 1} (9 x + 4) = \frac{9 x + 4}{9} - \frac{4}{9}$

Combine the numerators over the common denominator.

$f^{- 1} (9 x + 4) = \frac{9 x + 4 - 4}{9}$

Combine the opposite terms in $9 x + 4 - 4$ .

Subtract $4$ from $4$ .

$f^{- 1} (9 x + 4) = \frac{9 x + 0}{9}$

Add $9 x$ and $0$ .

$f^{- 1} (9 x + 4) = \frac{9 x}{9}$

Cancel the common factor of $9$ .

Cancel the common factor.

$f^{- 1} (9 x + 4) = \frac{9 x}{9}$

Divide $x$ by $1$ .

$f^{- 1} (9 x + 4) = x$

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

Set up the composite result function.

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

Evaluate $f (\frac{x}{9} - \frac{4}{9})$ by substituting in the value of $f^{- 1}$ into $f$ .

$f (\frac{x}{9} - \frac{4}{9}) = 9 (\frac{x}{9} - \frac{4}{9}) + 4$

Simplify each term.

Apply the distributive property.

$f (\frac{x}{9} - \frac{4}{9}) = 9 (\frac{x}{9}) + 9 (- \frac{4}{9}) + 4$

Cancel the common factor of $9$ .

Cancel the common factor.

$f (\frac{x}{9} - \frac{4}{9}) = 9 (\frac{x}{9}) + 9 (- \frac{4}{9}) + 4$

Rewrite the expression.

$f (\frac{x}{9} - \frac{4}{9}) = x + 9 (- \frac{4}{9}) + 4$

Cancel the common factor of $9$ .

Move the leading negative in $- \frac{4}{9}$ into the numerator.

$f (\frac{x}{9} - \frac{4}{9}) = x + 9 (\frac{- 4}{9}) + 4$

Cancel the common factor.

$f (\frac{x}{9} - \frac{4}{9}) = x + 9 (\frac{- 4}{9}) + 4$

Rewrite the expression.

$f (\frac{x}{9} - \frac{4}{9}) = x - 4 + 4$

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

Add $- 4$ and $4$ .

$f (\frac{x}{9} - \frac{4}{9}) = x + 0$

Add $x$ and $0$ .

$f (\frac{x}{9} - \frac{4}{9}) = x$

Since $f^{- 1} (f (x)) = x$ and $f (f^{- 1} (x)) = x$ , then $f^{- 1} (x) = \frac{x}{9} - \frac{4}{9}$ is the inverse of $f (x) = 9 x + 4$ .

$f^{- 1} (x) = \frac{x}{9} - \frac{4}{9}$

Find the Inverse f(x)=9x+4

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