已知x-y+3=0,求2xy-x^2-y^2+1的值

问题描述:

已知x-y+3=0,求2xy-x^2-y^2+1的值

x-y=﹣3
2xy-x²-y²+1
=﹣﹙x-y﹚²+1
=﹣﹙﹣3﹚²+1
=﹣9+1
=﹣8