What number goes in the box so that x^2 + 18x + 6x + ___ is the square of a binomial? If you find more than one, give your answer as a list.
x^2 + 18x + 6x + ____
x^2 + 24x + _____
Take (1/2) of 24 =12
Square it = 144
That's the missing number
Proof
(x + 12)^2 = x^2 + 24x + 144
P.S. - this proceedure is known as "completing the square "
