Question

find the inverse of $f(x) = 3x + 9$.

1. $y = 3x - 3$
2. $y = -3x - 9$
3. $y = \frac{x}{3} - 3$
4. $y = \frac{x + 9}{3}$

Explanation:

Step1: Replace $f(x)$ with $y$

$y = 3x +9$

Step2: Swap $x$ and $y$

$x = 3y +9$

Step3: Isolate $y$

Subtract 9 from both sides: $x-9 = 3y$
Divide by 3: $y=\frac{x-9}{3}=\frac{x}{3}-3$

Answer:

1. $y=\frac{x}{3}-3$