What is the inverse of the function

Question

y = 3x2 ?

Answer 1

If you mean y = 3x^2 then there is no inverse, since there are two values of x for every value of y.

However,

y/3 = x^2
x = √(y/3)

so, f ^-1(x) = √(x/3)

that will give you one side of the parabola, and -√(x/3) will give you the other side.