For what real values of s is 9x^2 + sx + 4 the square of a binomial?
(3x + 2 )^2 = 9x^2 + 12x + 4 s = 12
s = -12 is also a solution.
Square of binomial <=> Discriminant = 0
\(s^2 - 4(9)(4) = 0\\ s^2 = 144\\ s = \pm12\)
