For what real values of $c$ is $x^2 + 16x + c$ the square of a binomial? If you find more than one, then list your values separated by commas.
x^2 + 16x + c
Set the discriminant to 0 and solve for c
16^2 - 4(1)(c) = 0
256 - 4c = 0 add 4c to both sides
256 = 4c divide both sides by 4
64 = c