1) 2a + b + c = 9
2) a + 2b + c = 8
3) a + b + 2c = 11
multiply eq(2) by -2, add to eq(1):
2a + b + c = 9
-2a - 4b - 2c = -16
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- 3b - c = -7 (a)
multiply eq(2) by -1, add to eq(3):
-a - 2b - c = -8
a + b + 2c = 11
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- b + c = 3 (b)
add eq(a) to eq(b):
-3b - c = -7
-b + c = 3
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-4b = -4
b = -4/-4 = 1
using eq(b):
-1 + c = 3
c = 4
using eq(1):
2a + b + c = 9
2a + 1 + 4 = 9
2a = 4
a = 4/2 = 2
check using eq(2):
2 + 2(1) + 4 = 8
8 = 8
a = 2, b = 1, c = 4 or (2, 1, 4)