若x-y=2,xy=3,则代数式(x-1)(y+1)的值为
问题描述：
若x-y=2,xy=3,则代数式(x-1)(y+1)的值为
答
(x-1)(y+1)
=xy-（x-y）+1
=3-2+1
=2
答
(x-1)(y+1)
=xy-y+x-1
=xy+(x-y)-1
=3+2-1
=4