若x＜y＜0,试比较(x²＋y²)(x－y)与(x²－y²)(x＋y)的大小

若x＜y＜0,试比较(x²＋y²)(x－y)与(x²－y²)(x＋y)的大小
若x＜y＜0,试比较(x²＋y²)(x－y)与(x²－y²)(x＋y)的大小

若x＜y＜0,试比较(x²＋y²)(x－y)与(x²－y²)(x＋y)的大小
(x²+y²)(x-y)-(x²-y²)(x+y)
=(x²+y²)(x-y)-(x+y)(x-y)(x+y)
=(x-y)[(x²+y²)-(x+y)²]
=(x-y)(x²+y²-x²-2xy-y²)
=-2xy(x-y)
x

前面的大于后面的，令x=-2,y=-1