已知x+y=5,xy=-3,求多项式(2x-3y-4xy)-(x-4y+2xy)的值

问题描述:

已知x+y=5,xy=-3,求多项式(2x-3y-4xy)-(x-4y+2xy)的值

(2x-3y-4xy)-(x-4y+2xy)
=2x-3y-4xy-x+4y-2xy
=x+y-6xy
当x+y=5,xy=-3时
原式=5-6×(-3)
=35

(2x-3y-4xy)-(x-4y+2xy)
=2x-3y-4xy-x+4y-2xy
=x+y-6xy
=5-6×(-3)
=5+18
=23

原式=2x-3y-4xy-x+4y-2xy
=x+y-6xy
将 x+y=5 xy=-3
代入,得 5-6*(-3)
=5+18
=23