Question

若x＜y＜0,试比较（x^2+y^2)(x-y)与(x^2-y^2)(x+y)的大小.

Answer 1

（x^2+y^2)(x-y)-(x^2-y^2)(x+y)

=（x^2+y^2)(x-y)-(x-y)(x+y)^2

=[(x^2+y^2)-(x+y)^2](x-y)

=-2xy(x-y)

因为x