Question

Let f(x) = 2x + 2. Solve f-1(x) when x = 4.

Answer 1

$f(x)=2x+2 \\\\ f(x)-1= (2*4+2)-1 \\\\ =8+2-1= \\\\ =10-1= \\\\=\boxed{9}$

Answer 2

$f(x)=2x+2\\\\ f^{-1}(x):\\ y=2x+2\\ y-2=2x\ \ \ |Divide\ by\ 2\\ \frac{y-2}{2}=x\\\\ f^{-1}(x)=\frac{x-2}{2}\\ f^{-1}(4)=\frac{4-2}{2}=1\\\\ Solution\ is\ f^{-1}(4)=1$