喏x+y=6,xy=4 求(5x-4y-3xy)-(8x-y+2xy) 要全过程

问题描述:

喏x+y=6,xy=4 求(5x-4y-3xy)-(8x-y+2xy) 要全过程

(5x-4y-3xy)-(8x-y+2xy) =-3x-3y-5xy =-3(x+y)-5xy =-3*6-5*4 =-18-20 =-38

因为x+y=6 所以x=6-y 原式=[5(6-y)-4y-3xy]-[8(6-y)-y+2xy]=(30-9y-3xy)-(48-9y+2xy)=-18-5xy 因为xy=4所以原式=-38 给分!打字累半天…