Question

已知x+2Y=0，试求x的3次方+2xy(x+y)+4y的3次方-8的值。

Answer 1

x的3次方+2xy(x+y)+4y的3次方-8
=x³+2x²y+2xy²+4y³-8
=x²（x+2y）+2y²（x+2y）-8
把x+2y换成0
原式=-8

Answer 2

x^3+2xy(x+y)+4y^3-8
=x^3+2xy(x+y)+4y^3-8
=(-2y)^3+2(-2y)*y(-2y+y)+4y^3-8
=-8y^3-4y^2*(-y)+4y^3-8
=-8y^3+4y^3+4y^3-8
=0-8
=-8