(1){4s+3t=5,{2s-t=-5;(2){5x-6y=9,{7x-4y=-5.

问题描述:

(1){4s+3t=5,
{2s-t=-5;
(2){5x-6y=9,
{7x-4y=-5.

4s+3t=5①2s-t=-5②先用②×2得:4s-2t=-10③③-①得:(4s-2t)-(4s+3t) =-10-5-2t-3t=-15-5t=-15t=3把t=3带入②得:2s-3=-5s=-1所以,s=-1,t=35x-6y=9 ①7x-4y=-5 ②①×7得:35x-42y=63 ③②×5得:35x-20y=-25④...