# Math Help - Functions

1. ## Functions

f(x) = 3x-2
if f(a)=4 determine the numerical value of f-1(4)
I'm really clueless on how to do this one.
I started with:
4 = 3x-2
x = 2

and then tried substituting that into the inverse which is y = (x+2)/3
to get: 2+2/3 = 4/3 = 1.333....
could anyone tell me if I did this correctly?

2. Originally Posted by xxlvh
f(x) = 3x-2
if f(a)=4 determine the numerical value of f-1(4)
I'm really clueless on how to do this one.
I started with:
4 = 3x-2
x = 2

and then tried substituting that into the inverse which is y = (x+2)/3
to get: 2+2/3 = 4/3 = 1.333....

could anyone tell me if I did this correctly?
the last part is off. you're working so hard, you already passed your stop. you simply have to find the "a", which you did. it's 2

remember, if $f(a) = 4$ we would have $f^{-1}(4) = a$ by taking the inverse function of both sides of the equation.