Find the Inverse f(x)=5x+8

$f (x) = 5 x + 8$

Step 1

Write $f (x) = 5 x + 8$ as an equation.

$y = 5 x + 8$

Step 2

Interchange the variables.

$x = 5 y + 8$

Step 3

Solve for $y$ .

Rewrite the equation as $5 y + 8 = x$ .

$5 y + 8 = x$

Subtract $8$ from both sides of the equation.

$5 y = x - 8$

Divide each term in $5 y = x - 8$ by $5$ and simplify.

Divide each term in $5 y = x - 8$ by $5$ .

$\frac{5 y}{5} = \frac{x}{5} + \frac{- 8}{5}$

Simplify the left side.

Cancel the common factor of $5$ .

Cancel the common factor.

$\frac{5 y}{5} = \frac{x}{5} + \frac{- 8}{5}$

Divide $y$ by $1$ .

$y = \frac{x}{5} + \frac{- 8}{5}$

Simplify the right side.

Move the negative in front of the fraction.

$y = \frac{x}{5} - \frac{8}{5}$

Step 4

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

$f^{- 1} (x) = \frac{x}{5} - \frac{8}{5}$

Step 5

Verify if $f^{- 1} (x) = \frac{x}{5} - \frac{8}{5}$ is the inverse of $f (x) = 5 x + 8$ .

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 $f^{- 1} (5 x + 8)$ by substituting in the value of $f$ into $f^{- 1}$ .

$f^{- 1} (5 x + 8) = \frac{5 x + 8}{5} - \frac{8}{5}$

Combine the numerators over the common denominator.

$f^{- 1} (5 x + 8) = \frac{5 x + 8 - 8}{5}$

Combine the opposite terms in $5 x + 8 - 8$ .

Subtract $8$ from $8$ .

$f^{- 1} (5 x + 8) = \frac{5 x + 0}{5}$

Add $5 x$ and $0$ .

$f^{- 1} (5 x + 8) = \frac{5 x}{5}$

Cancel the common factor of $5$ .

Cancel the common factor.

$f^{- 1} (5 x + 8) = \frac{5 x}{5}$

Divide $x$ by $1$ .

$f^{- 1} (5 x + 8) = x$

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

Set up the composite result function.

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

Evaluate $f (\frac{x}{5} - \frac{8}{5})$ by substituting in the value of $f^{- 1}$ into $f$ .

$f (\frac{x}{5} - \frac{8}{5}) = 5 (\frac{x}{5} - \frac{8}{5}) + 8$

Simplify each term.

Apply the distributive property.

$f (\frac{x}{5} - \frac{8}{5}) = 5 (\frac{x}{5}) + 5 (- \frac{8}{5}) + 8$

Cancel the common factor of $5$ .

Cancel the common factor.

$f (\frac{x}{5} - \frac{8}{5}) = 5 (\frac{x}{5}) + 5 (- \frac{8}{5}) + 8$

Rewrite the expression.

$f (\frac{x}{5} - \frac{8}{5}) = x + 5 (- \frac{8}{5}) + 8$

Cancel the common factor of $5$ .

Move the leading negative in $- \frac{8}{5}$ into the numerator.

$f (\frac{x}{5} - \frac{8}{5}) = x + 5 (\frac{- 8}{5}) + 8$

Cancel the common factor.

$f (\frac{x}{5} - \frac{8}{5}) = x + 5 (\frac{- 8}{5}) + 8$

Rewrite the expression.

$f (\frac{x}{5} - \frac{8}{5}) = x - 8 + 8$

Combine the opposite terms in $x - 8 + 8$ .

Add $- 8$ and $8$ .

$f (\frac{x}{5} - \frac{8}{5}) = x + 0$

Add $x$ and $0$ .

$f (\frac{x}{5} - \frac{8}{5}) = x$

Since $f^{- 1} (f (x)) = x$ and $f (f^{- 1} (x)) = x$ , then $f^{- 1} (x) = \frac{x}{5} - \frac{8}{5}$ is the inverse of $f (x) = 5 x + 8$ .

$f^{- 1} (x) = \frac{x}{5} - \frac{8}{5}$

Find the Inverse f(x)=5x+8

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