已知:x+y=1,xy=-1/2,则x(x+y)(x-y)-x(x+y)^2=

问题描述:

已知:x+y=1,xy=-1/2,则x(x+y)(x-y)-x(x+y)^2=

x(x+y)(x-y)-x(x+y)^2
=x(x+y)〔(x-y)-(x+y)〕
=x(x+y)(-2y)
=-2xy(x+y)
把x+y=1,xy=-1/2代入-2xy(x+y)可得:
-2xy(x+y)
=-2*(-1/2)*1
=1