Find the Inverse f(k)=5x+7

$f (k) = 5 x + 7$

Step 1

Write $f (k) = 5 x + 7$ as an equation.

$y = 5 x + 7$

Step 2

Interchange the variables.

$x = 5 y + 7$

Step 3

Solve for $y$ .

Rewrite the equation as $5 y + 7 = x$ .

$5 y + 7 = x$

Subtract $7$ from both sides of the equation.

$5 y = x - 7$

Divide each term in $5 y = x - 7$ by $5$ and simplify.

Divide each term in $5 y = x - 7$ by $5$ .

$\frac{5 y}{5} = \frac{x}{5} + \frac{- 7}{5}$

Simplify the left side.

Cancel the common factor of $5$ .

Cancel the common factor.

$\frac{5 y}{5} = \frac{x}{5} + \frac{- 7}{5}$

Divide $y$ by $1$ .

$y = \frac{x}{5} + \frac{- 7}{5}$

Simplify the right side.

Move the negative in front of the fraction.

$y = \frac{x}{5} - \frac{7}{5}$

Step 4

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

$f^{- 1} (x) = \frac{x}{5} - \frac{7}{5}$

Step 5

Verify if $f^{- 1} (x) = \frac{x}{5} - \frac{7}{5}$ is the inverse of $f (x) = 5 x + 7$ .

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 $f^{- 1} (5 x + 7)$ by substituting in the value of $f$ into $f^{- 1}$ .

$f^{- 1} (5 x + 7) = \frac{5 x + 7}{5} - \frac{7}{5}$

Combine the numerators over the common denominator.

$f^{- 1} (5 x + 7) = \frac{5 x + 7 - 7}{5}$

Combine the opposite terms in $5 x + 7 - 7$ .

Subtract $7$ from $7$ .

$f^{- 1} (5 x + 7) = \frac{5 x + 0}{5}$

Add $5 x$ and $0$ .

$f^{- 1} (5 x + 7) = \frac{5 x}{5}$

Cancel the common factor of $5$ .

Cancel the common factor.

$f^{- 1} (5 x + 7) = \frac{5 x}{5}$

Divide $x$ by $1$ .

$f^{- 1} (5 x + 7) = x$

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

Set up the composite result function.

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

Evaluate $f (\frac{x}{5} - \frac{7}{5})$ by substituting in the value of $f^{- 1}$ into $f$ .

$f (\frac{x}{5} - \frac{7}{5}) = 5 (\frac{x}{5} - \frac{7}{5}) + 7$

Simplify each term.

Apply the distributive property.

$f (\frac{x}{5} - \frac{7}{5}) = 5 (\frac{x}{5}) + 5 (- \frac{7}{5}) + 7$

Cancel the common factor of $5$ .

Cancel the common factor.

$f (\frac{x}{5} - \frac{7}{5}) = 5 (\frac{x}{5}) + 5 (- \frac{7}{5}) + 7$

Rewrite the expression.

$f (\frac{x}{5} - \frac{7}{5}) = x + 5 (- \frac{7}{5}) + 7$

Cancel the common factor of $5$ .

Move the leading negative in $- \frac{7}{5}$ into the numerator.

$f (\frac{x}{5} - \frac{7}{5}) = x + 5 (\frac{- 7}{5}) + 7$

Cancel the common factor.

$f (\frac{x}{5} - \frac{7}{5}) = x + 5 (\frac{- 7}{5}) + 7$

Rewrite the expression.

$f (\frac{x}{5} - \frac{7}{5}) = x - 7 + 7$

Combine the opposite terms in $x - 7 + 7$ .

Add $- 7$ and $7$ .

$f (\frac{x}{5} - \frac{7}{5}) = x + 0$

Add $x$ and $0$ .

$f (\frac{x}{5} - \frac{7}{5}) = x$

Since $f^{- 1} (f (x)) = x$ and $f (f^{- 1} (x)) = x$ , then $f^{- 1} (x) = \frac{x}{5} - \frac{7}{5}$ is the inverse of $f (x) = 5 x + 7$ .

$f^{- 1} (x) = \frac{x}{5} - \frac{7}{5}$

Find the Inverse f(k)=5x+7

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