因式分解-x^3+2x^2y-xy^2和16(x-y)^2-9(x+y)^2和(x+2)（x+4）+x^2-4
问题描述：
因式分解-x^3+2x^2y-xy^2和16(x-y)^2-9(x+y)^2和(x+2)（x+4）+x^2-4
答
-x^3+2x^2y-xy^2
=-x(x²-2xy+y²)
=-x(x-y)²
16(x-y)^2-9(x+y)^2
=[4(x-y)]²-[3(x+y)]²
=(4x-4y)²-(3x+3y)²
=[4x-4y-(3x+3y)][4x-4y+(3x+3y)]
=(x-7y)(7x-y)
(x+2)（x+4）+x^2-4
=(x+2)（x+4）+(x-2)(x+2)
=(x+2)[（x+4）+(x-2)]
=(x+2)（2x+2)
=2(x+2)（x+1)
答
1)-x(x^2-2xy+y^2)=-x(x-y)^2
2)展开得7x^2-50xy+7y^2=(7x-y)(x-7y)
3)x^2+6x+8+x^2-4=2(x+1)(x+2)