-20 = 4a - 2b + c
-4 = c
-20 = 16a + 4b + c
4a - 2b + c = 16a + 4b + c
4a - 2b = 16a + 4b
-6b = 12a
b = -2a
-20 = 4a - 2b + c
-20 = 4a + 4a - 4
-16 = 8a
-2 = a
b = 4
c = -4
y = -2x^2 + 4x - 4
y = -2 (x^2 - 2x) - 4
y = -2 (x^2 - 2x + 1 - 1) - 4
y = -2 (x^2 - 2x + 1) + 2 - 4
y = -2 (x + 1)^2 - 2
