Find the constant $p$ such that $x^2 - 5x - 2x + 10x + p$ is the square of a binomial.
x^2 + 8x + p
p = (1/2 the coefficient on x )^2 = (8/2)^2 = 4^2 = 16
So
x^2 + 8x + 16 =
(x + 4) ( x + 4) =
(x + 4)^2
+1046 
