If f(x)=ax2+bx+cf(x) = ax^2 + bx + cf(x)=ax2+bx+c has a vertex at (h,k)(h, k)(h,k), which of the following is true for f−1(x)f^{-1}(x)f−1(x)?
It is a function on R\mathbb{R}R
It is a function if restricted to x≥hx \geq hx≥h
It is always x2x^2x2
It does not exist