-(x2+y2)+[-3xy-(x2-y2)],其中x =-1,y =2.

问题描述:

-(x2+y2)+[-3xy-(x2-y2)],其中x =-1,y =2.

-(x2+y2)+[-3xy-(x2-y2)]
=-x²-y²-3xy-x²+y²
=-2x²-3xy
=-2×(-1)²-3×(-1)×2
=4