已知x-y=1,求x2-y2+x-3y的值.
问题描述:
已知x-y=1,求x2-y2+x-3y的值.
答
∵x-y=1,
∴x2-y2+x-3y
=(x+y)(x-y)+x-3y,
=x+y+x-3y,
=2x-2y,
=2(x-y),
=2.