已知y2-5y=20,求(y-1)(2y-1)-(y+1)2+1的值.

问题描述:

已知y2-5y=20,求(y-1)(2y-1)-(y+1)2+1的值.

∵y2-5y=20,
∴(y-1)(2y-1)-(y+1)2+1,
=2y2-3y+1-y2-2y-1+1,
=y2-5y+1,
=20+1,
=21.