已知X+Y=6,XY=-4,求(5X-4Y-3XY)-(8X-Y+2XY)的值

问题描述:

已知X+Y=6,XY=-4,求(5X-4Y-3XY)-(8X-Y+2XY)的值

(5X-4Y-3XY)-(8X-Y+2XY)=-3X-3Y-5XY
因为X+Y=6,XY=-4,所以(5X-4Y-3XY)-(8X-Y+2XY)=-3X-3Y-5XY=-18+20=2

(5X-4Y-3XY)-(8X-Y+2XY)
=-(3X+3Y)-5XY=-3*6+4*5=2