(2x+y)^2-9(x+2y)^2

问题描述:

(2x+y)^2-9(x+2y)^2

(2x+y)^2-9(x+2y)^2
=(2x+y+3x+6y)(2x+y-3x-6y)
= (5x+7y)( -x-5y)
=-(5x+7y)( x+5y)