Solve the third equation for x.
-2x - 2z = 62
-2x = 62 + 2z
x = (62 + 2z) / -2
x = -31 - z
Substitute this expression in for x in the first equation.
-x - 5y - z = 211
-(-31 - z) - 5y - z = 211
31 + z - 5y - z = 211
31 - 5y = 211
-5y = 180
y = 180 / -5
y = -36
Now substitute (-31 - z) in for x and -36 in for y in the second equation and solve for z.
11x + 8y - 5z = -213
11(-31 - z) + 8(-36) - 5z = -213
-341 - 11z - 288 - 5z = -213
-629 - 16z = -213
-16z = 416
z = -26
We know from the third equation that x = -31 - z. Substitute -26 in for z and solve for x.
x = -31 - z
x = -31 - (-26)
x = -5
Solution: {x = -5, y = -36, z = -26}
Check these answers using substitution.
-x - 5y - z = 211
-(-5) - 5(-36) - (-26) = 211
211 = 211
11x + 8y - 5z = -213
11(-5) + 8(-36) - 5(-26) = -213
-213 = -213
-2x - 2z = 62
-2(-5) - 2(-26) = 62
62 = 62
The solutions work in all three equations.
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