Question

If (x) and f-1(x) are inverse functions of each other and f(X) =2X+5 what is f-1(8)

Answer 1

f(x)=2x+5
We can rewrite as y = 2x +5.
We need to find x.
y=2x+5
y-5 = 2x
x=(y-5)/2

Now we need exchange y by x, and x by y.
x=(y-5)/2
y=(x-5)/2

f⁻¹(x)= (x-5)/2
f⁻¹(8)= (8-5)/2= 3/2 =1.5

f⁻¹(8)=3/2 or f⁻¹(8)=1.5