Question

计算（x-y/x+2y）^3

我才初二。。只教了平方差公式和完全平方公式。。 能不能用我们已教的知识计算啊

Answer 1

(x-y)^3
=(x-y)(x-y)^2
=(x-y)(x^2-2xy+y^2)
=x(x^2-2xy+y^2)-y(x^2-2xy+y^2)
=x^3-2x^2y+xy^2-x^2y+2xy^2-y^3
=x^3-3x^2y+3xy^2-y^3
分母一样计算
=(x^3-3x^2y+3xy^2-y^3)/(x^3+6x^2y+12xy^2+8y^3)