You could also use PSF (product, sum, factors)
4x^2 + 17xy + 15y^2
P: first+last 15*4
S: middle
F: what two numbers multiply together to get 60 and add together to get 17?
P: 60
S: 17
F: 12,5
Break the middle into two different parts based on the factors:
4x^2 + 12xy + 5xy + 15y^2
4x^2 +...