{2x-y-z=3{4x+2y-z=15{4x+3y=18

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{2x-y-z=3{4x+2y-z=15{4x+3y=18
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{2x-y-z=3{4x+2y-z=15{4x+3y=18
{2x-y-z=3
{4x+2y-z=15
{4x+3y=18

{2x-y-z=3{4x+2y-z=15{4x+3y=18
2x-y-z=3 (1)
4x+2y-z=15 (2)
4x+3y=18 (3)
(2)-(1)
2x+3y=12 (4)
(3)-(4)
2x=6
x=3
y=(18-4x)/3=2
z=2x-y-3=1

2x-y-z=3 ①
4x+2y-z=15 ②
4x+3y=18 ③
③-②得 y+z=3
代入①得 2x-3=3
所以x=3 代入③
y=2 代入②
z=1