5x+3y=25 2x+7y-3z=19 3x+2y-z=18
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5x+3y=25 2x+7y-3z=19 3x+2y-z=18
5x+3y=25 2x+7y-3z=19 3x+2y-z=18
5x+3y=25 2x+7y-3z=19 3x+2y-z=18
(3)×3-(2)得
7x-y=35 (4)
(4)×3+(1)得
12x=60
∴x=5
把x=5代入(1)得
y=0
把x=5,y=0代入(3)得
15+0-z=18
∴z=-3
∴方程组的解是
x=5
y=0
z=-3
2x+7y-3z=19 ……(1)
3x+2y-z=18,9x+6y-3z=48……(2)
(2)-(1)得:7x-y=29,21x-3y=87……(3)
5x+3y=25 ……(4)
(3)+(4)得:26x=112,x=112/26=56/13
∴y=7x-29=7×56/13-29=392/13-377/13=15/13
∴z=3x+2y-18=3×56/13+2×15/13-18=198/13-234/13=-36/13
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