先化简,再求值:(x²-2y²)(x+2y)-2xy(x-y),其中x=负2,y=1/2.

问题描述:

先化简,再求值:(x²-2y²)(x+2y)-2xy(x-y),其中x=负2,y=1/2.

=x^3+2yx^2-2xy^2-4y^3-2yx^2+2xy^2
=x^3-4y^3
代入
=-2^3-4*(1/2)^3
=-17/2