For what real values of $a$ is $x^2 + ax + 25$ the square of a binomial? If you find more than one, then list your values in increasing order, separated by commas.
x^2 + ax + 25
Just like an earlier problem, set the discriminant to 0 and solve for a
So we have
a^2 - 4(1)(25) = 0
a^2 - 100 = 0 factor this
(a - 10) (a + 10) = 0
Setting both factors to 0 and solving for a gives a = 10 or a = -10
So
a = -10, 10
+612 
