已知 x+y=3,xy=-2,求(3x-2y+8xy)-(x-4y-5xy)的值

问题描述:

已知 x+y=3,xy=-2,求(3x-2y+8xy)-(x-4y-5xy)的值

(3x-2y+8xy)-(x-4y-5xy)
=3x-2y+8xy-x+4y+5xy
=2x+2y+13xy
=2(x+y)+13xy
=2×3+13×(-2)
=-20