
William W. answered 05/13/19
Math and science made easy - learn from a retired engineer
The basic equation for a parabola (quadratic function) is f(x) = a(x - h)2 + k where the vertex is at the point (h, k). Since the origin (0, 0) is the vertex, we can plug in 0 for h and k so the equation becomes f(x) = a(x - 0)2 + 0 or f(x) = ax2
Since we know that (4, -64) is a point on the curve, then f(4) must equal -64 so we can plug in those values for x and y to get -64 = a(4)2 then we can solve for a: -64 = 16a or a = -64/16 = -4 so the function is:
f(x) = -4x2