(x-2y)(x+2y)-(x+3y)的平方

问题描述:

(x-2y)(x+2y)-(x+3y)的平方

(x-2y)(x+2y)-(x+3y)^2
=x^2-4y^2-x^2-6xy-9y^2
=-13y^2-6xy
=-y(13y+6x)