So we want to know which of the following functions has an inverse function. So an inverse function is a function that "reverses" another function. We need to put y instead of x and x instead of y. So for the first case: y=x is x=y so this function has an inverse function. y=x^2 is x=y^2 so y=sqrt(x). y=x^3 is x=y^3 so y=∛x. y=x^4 so x=y^4, y=4√x or forth root of x. So all of our functions have an inverse function.
