1.用加减消元法解下列方程组:(1)｛7x-2y=3,9x+2y=-19;(2)｛6x-5y=3,6x+y=-15;(3)｛4s+3t=5,2s-t=-5;

题目

1.用加减消元法解下列方程组:(1)｛7x-2y=3,9x+2y=-19;(2)｛6x-5y=3,6x+y=-15;(3)｛4s+3t=5,2s-t=-5;
4)｛5x-6y=9,7x-4y=-5.

答案

:(1)｛7x-2y=3,9x+2y=-19
7x-2y+9x+2y=3-19
16x=-16
x=-1
y=-5
(2)｛6x-5y=3,6x+y=-15
6x-5y-6x-y=3+15
-6y=18
y=-3
x=-2
(3)｛4s+3t=5,2s-t=-5;
4s+3t+3(2s-t)=5-3*5
10s=-10
s=-1
t=3
4)｛5x-6y=9,7x-4y=-5
2(5x-6y)-3(7x-4y)=2*9-3*(-5)
10x-12y-21x+12=18+15
-11x=33
x=-3
y=-4