Thread: Cubic function

A cubic function has turning points at (0,0) and (3,-8). The derived function must be a quadratic function: k(x-0)(x-3). Can the turning point of the quadratic function be found? I don't think I have studied how to get the cubic function which would help.

Perhaps the lower turning point should be (3,-18) and then the equation is (x-0)(x-0)(x-5).