6(x+y)的平方-11(x+y)(x-y)+3(x-y)的平方=?

6(x+y)的平方-11(x+y)(x-y)+3(x-y)的平方=?

原式=[2(x+y)-3(x-y)][3(x+y)-(x-y)]
=(-x+5y)(2x+4y)
=-2(x-5y)(x+2y)