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

3(x+y)(x-y)+4(x-y)^2
= (x-y)[3(x+y) + 4(x-y)]
= (x-y)(7x-y)
= 7x^2 -8xy + y^2

如果是因式分解应该是：
3(x+y)(x-y)+4(x-y)^2=
（x-y)[3(x+y)+4(x-y)]
=(x-y)(7x-y)

3(x+y)(x-y)+4(x-y)^2
= (x-y)[3(x+y) + 4(x-y)]
= (x-y)[7x-y]
= 7x^2 -8xy + y^2

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

原示=(X-Y)[3(X+Y)+4(X-Y)]=
3(X+Y)+4(X-Y)=7X-Y
所以原示(X-Y)(7X-Y)=7X^2-XY-7XY+Y^2=7X^2-8XY+Y^2