3x-4y+2xy)--(2x--5y+5xy)=当x+y=5,xy=-3

问题描述:

3x-4y+2xy)--(2x--5y+5xy)=当x+y=5,xy=-3

(3x-4y+2xy)--(2x--5y+5xy)
=3x-4y+2xy-2x+5y-5xy
=x+y-3xy
=5-3*(-3)
=5+9
=14