x+y=-5,xy=2,求多项式2x-3y-4xy与x-4y-8xy的差的值(顺便讲解一下,

问题描述:

x+y=-5,xy=2,求多项式2x-3y-4xy与x-4y-8xy的差的值(顺便讲解一下,

=2x-3y-4xy-x+4y+8xy
=x+y+4xy
=-5+8
=3


(2x--3y-4xy)-(x-4y-8xy)
=2x-3y-4xy-x+4y+8xy
=x+y+4xy
=(x+y)+4xy
=-5+4*2
=-5+8
=3