已知x-y=3,xy=-1,求(2x+3y-2xy)-(x+4y+xy)-(3xy+2y-2x)的值

问题描述:

已知x-y=3,xy=-1,求(2x+3y-2xy)-(x+4y+xy)-(3xy+2y-2x)的值

(2x+3y-2xy)-(x+4y+xy)-(3xy+2y-2x)
=2x+3y-2xy-x-4y-xy-3xy-2y+2x
=3x-3y-6xy
=3(x-y-2xy)
x-y=3,xy=-1代入=3*(3+2)=15