math
posted by Hasane .
A student was asked to find the inverse of the function f(x)=3x7.
The student began the solution with the following:
Write f(x) = 3x7 as y = 3x7
x= 3y7
The student eventually got the right answer for f^(1)(x) [inverse notation] but did not get full marks for the solution. Why not?

he got x as a function of y, but did not illustrate that
f^1(x) = (x+7)/3