x + 2y + 3z = 5
2x - y - z = 1
x + 3y + 4z = 6
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- x - 3y - 4z = - 6
- y - z = - 1
y = 1 - z
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2x - y - z = 1
2x = 1 + y + z
2x = 1 + 1 - z + z
2x = 2
x = 1
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x + 2y + 3z = 5
1 + 2( 1 - z ) + 3z = 5
1 + 2 - 2z + 3z = 5
z = 5 - 3
z = 2
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y = 1 - z
y = 1 - 2
y = - 1
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ОТВЕТ x = 1 ; y = - 1 ; z = 2