Find the equation whose graph is a parabola with vertex (2,4), vertical axis of symmetry, and contains the point (1,-1). Express your answer in the form "ax^2+bx+c".
Vertex form will be
a (x-2)^2 + 4 = y contains the point 1,-1 substitute this in
a (1-2)^2 + 4 = -1
a + 4 = -1 so a = -5
-5 ( x-2)^2 +4 = y
-5x^2 +20x-16 = y
