先化简,再求值(x-2y)(x方+2xy+4y方)-x(x-y)(x+y)+(2y）的三次方,x=5,y=-2
问题描述：
先化简,再求值(x-2y)(x方+2xy+4y方)-x(x-y)(x+y)+(2y）的三次方,x=5,y=-2
答
(x-2y)(x方+2xy+4y方)-x(x-y)(x+y)+(2y）的三次方
=x³-(2y)³-x(x²-y²)+(2y)³
=x³-x³+xy²
=xy²
=5×(-2)²
=5×4
=20