What number goes in the box so that the quadratic is the square of a binomial? 9x^2 + 6x + ___ + x^2 + 4x.
Combine like terms to get 10x^2+10x+?, but we want a binomial.
So we fill in (10x+1/2)^2 to get 10x^2 and 10x, but the number we need is 1/4 to make it a binomial
1/4 is the number that goes in the box