Use the form ax^2 + bx +c to find values for a, b and c:
a = -1, b = -10 and c = -20
The vertex form is written as a(x+d)^2 +e
d = b/2a = -10/2*-1 = 5
e = c-b^2/4a = -20 - /-10^2/4*-1 = 5
Replace the letters with their values in the vertex form formula:
-(x+5)^2 + 5
The third choice is the correct one.
