若x<y<0,试比较(x²+y²)*(x-y)与(x²-y²)*(x+y)的大小
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(x²+y²)(x-y)-(x²-y²)(x+y)
=(x²+y²)(x-y)-(x+y)(x-y)(x+y)
=(x²+y²)(x-y)-(x+y)²(x-y)
=(x-y)[x²+y²-(x+y)²]
=(x-y)[x²+y²-(x²+2xy+y²)]
=(x-y)(-2xy)
=2xy(y-x)
∵x<y<0
∴xy>0,y-x>0
∴(x²+y²)(x-y)-(x²-y²)(x+y)>0
∴(x²+y²)(x-y)>(x²-y²)(x+y)
望采纳,O(∩_∩)O谢谢
(x²+y²)(x-y)-(x²-y²)(x+y)
=(x²+y²)(x-y)-(x+y)(x-y)(x+y)
=(x²+y²)(x-y)-(x+y)²(x-y)
=(x-y)[x²+y²-(x+y)²]
=(x-y)[x²+y²-(x²+2xy+y²)]
=(x-y)(-2xy)
=2xy(y-x)
∵x<y<0
∴xy>0,y-x>0
∴(x²+y²)(x-y)-(x²-y²)(x+y)>0
∴(x²+y²)(x-y)>(x²-y²)(x+y)
望采纳,O(∩_∩)O谢谢
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