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

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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.

优质解答：

:(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

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