(2x+y)(2x-y)-(3x-2y)(x+y)-y(2x-y)

(2x+y)(2x-y)-(3x-2y)(x+y)-y(2x-y)
=4x2-y2-(3x2+3xy-2xy-2y2)-2xy-y2
=4x2-y2-3x2-3xy+2xy+2y2-2xy+y2
=(4x2-3x2)-(y2-y2-2y2)-(3xy-2xy+2xy)
=x2+2y2-3xy
（后面那个大2指的是平方）
如果不是因式分解的话，这样就没什么错了

(2x+y)(2x-y)-(3x-2y)(x+y)-y(2x-y)
=(4x^2-y^2)-(3x^2-2xy+3xy-2y^2)-(2xy-y^2)
=(4x^2-3x^2)+(2xy-3xy-2xy)+(-y^2+2y^2+y^2)
=x^2-3xy+2y^2
若是因式分解,再等下去
=(x-y)(x-2y)

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