+713 For what real values of $c$ is $x^2 - 8x - 4x + c + x^2 - 20x + x^2$ the square of a binomial?
+24 Combine like terms
2x^2 - 32x + c
binomial square expansion says that (a+b)^2 = a^2 + 2ab + b^2
so a = sqrt2 * x
2ab = 2 * sqrt2 * x * sqrt(c)
-32x = 2 * sqrt2 * x * sqrt(c)
-16 = sqrt(2c)
256 = 2c
c = 128
