Algebra Examples

$f (x) = 7 x + 2$

Step 1

Write $f (x) = 7 x + 2$ as an equation.

$y = 7 x + 2$

Step 2

Interchange the variables.

$x = 7 y + 2$

Step 3

Solve for $y$ .

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Step 3.1

Rewrite the equation as $7 y + 2 = x$ .

$7 y + 2 = x$

Step 3.2

Subtract $2$ from both sides of the equation.

$7 y = x - 2$

Step 3.3

Divide each term in $7 y = x - 2$ by $7$ and simplify.

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Step 3.3.1

Divide each term in $7 y = x - 2$ by $7$ .

$\frac{7 y}{7} = \frac{x}{7} + \frac{- 2}{7}$

Step 3.3.2

Simplify the left side.

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Step 3.3.2.1

Cancel the common factor of $7$ .

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Step 3.3.2.1.1

Cancel the common factor.

$\frac{7 y}{7} = \frac{x}{7} + \frac{- 2}{7}$

Step 3.3.2.1.2

Divide $y$ by $1$ .

$y = \frac{x}{7} + \frac{- 2}{7}$

Step 3.3.3

Simplify the right side.

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Step 3.3.3.1

Move the negative in front of the fraction.

$y = \frac{x}{7} - \frac{2}{7}$

Step 4

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

$f^{- 1} (x) = \frac{x}{7} - \frac{2}{7}$

Step 5

Verify if $f^{- 1} (x) = \frac{x}{7} - \frac{2}{7}$ is the inverse of $f (x) = 7 x + 2$ .

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Step 5.1

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

Step 5.2

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

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Step 5.2.1

Set up the composite result function.

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

Step 5.2.2

Evaluate $f^{- 1} (7 x + 2)$ by substituting in the value of $f$ into $f^{- 1}$ .

$f^{- 1} (7 x + 2) = \frac{7 x + 2}{7} - \frac{2}{7}$

Step 5.2.3

Combine the numerators over the common denominator.

$f^{- 1} (7 x + 2) = \frac{7 x + 2 - 2}{7}$

Step 5.2.4

Combine the opposite terms in $7 x + 2 - 2$ .

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Step 5.2.4.1

Subtract $2$ from $2$ .

$f^{- 1} (7 x + 2) = \frac{7 x + 0}{7}$

Step 5.2.4.2

Add $7 x$ and $0$ .

$f^{- 1} (7 x + 2) = \frac{7 x}{7}$

Step 5.2.5

Cancel the common factor of $7$ .

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Step 5.2.5.1

Cancel the common factor.

$f^{- 1} (7 x + 2) = \frac{7 x}{7}$

Step 5.2.5.2

Divide $x$ by $1$ .

$f^{- 1} (7 x + 2) = x$

Step 5.3

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

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Step 5.3.1

Set up the composite result function.

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

Step 5.3.2

Evaluate $f (\frac{x}{7} - \frac{2}{7})$ by substituting in the value of $f^{- 1}$ into $f$ .

$f (\frac{x}{7} - \frac{2}{7}) = 7 (\frac{x}{7} - \frac{2}{7}) + 2$

Step 5.3.3

Simplify each term.

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Step 5.3.3.1

Apply the distributive property.

$f (\frac{x}{7} - \frac{2}{7}) = 7 (\frac{x}{7}) + 7 (- \frac{2}{7}) + 2$

Step 5.3.3.2

Cancel the common factor of $7$ .

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Step 5.3.3.2.1

Cancel the common factor.

$f (\frac{x}{7} - \frac{2}{7}) = 7 (\frac{x}{7}) + 7 (- \frac{2}{7}) + 2$

Step 5.3.3.2.2

Rewrite the expression.

$f (\frac{x}{7} - \frac{2}{7}) = x + 7 (- \frac{2}{7}) + 2$

Step 5.3.3.3

Cancel the common factor of $7$ .

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Step 5.3.3.3.1

Move the leading negative in $- \frac{2}{7}$ into the numerator.

$f (\frac{x}{7} - \frac{2}{7}) = x + 7 (\frac{- 2}{7}) + 2$

Step 5.3.3.3.2

Cancel the common factor.

$f (\frac{x}{7} - \frac{2}{7}) = x + 7 (\frac{- 2}{7}) + 2$

Step 5.3.3.3.3

Rewrite the expression.

$f (\frac{x}{7} - \frac{2}{7}) = x - 2 + 2$

Step 5.3.4

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

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Step 5.3.4.1

Add $- 2$ and $2$ .

$f (\frac{x}{7} - \frac{2}{7}) = x + 0$

Step 5.3.4.2

Add $x$ and $0$ .

$f (\frac{x}{7} - \frac{2}{7}) = x$

Step 5.4

Since $f^{- 1} (f (x)) = x$ and $f (f^{- 1} (x)) = x$ , then $f^{- 1} (x) = \frac{x}{7} - \frac{2}{7}$ is the inverse of $f (x) = 7 x + 2$ .

$f^{- 1} (x) = \frac{x}{7} - \frac{2}{7}$