f(x) = 1/2x +4
replace f(x) with y
y = 1/2x+4
switch x and y
x = 1/2y +4
solve for y
multiply both sides by 2
2x = y+8
subtract 8 from both sides
2x-8 = y
rewrite with y on the left side: y = 2x-8
replace y with f(x)^-1 (inverse notation)
f(x)^-1 = 2x-8
solve for f^-1(4)
replace x with 4 in the equation and solve:
2(4) -8 = 8-8 = 0
