利用作差法,比较当Y<0时,比较A=x³-(2x²y-y²-3y)与B=x³-2x²y+y²+2y的大小

问题描述:

利用作差法,比较当Y<0时,比较A=x³-(2x²y-y²-3y)与B=x³-2x²y+y²+2y的大小

A-B=x³-(2x²y-y²-3y)-(x³-2x²y+y²+2y)
=x³-2x²y+y²+3y-x³+2x²y-y²-2y
=3y-2y
=y
因为Y<0,所以A-B<0,即A<B.