SOLUTION: Solve the system of equations 3x+4y+z=7 2y+z=3 -5x+3y+8z=-31

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Question 1012903: Solve the system of equations
3x+4y+z=7
2y+z=3
-5x+3y+8z=-31
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
3x+4y+z=7
2y+z=3 --> z = -2y+3
-5x+3y+8z=-31
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Sub for z in the 1st & 3rd equations.
3x+4y+z=7 --> 3x + 4y - 2y + 3 = 7 --> 3x + 2y = 4 Eqn A
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-5x+3y+8z=-31 --> -5x + 3y - 16y + 24 = -31 --> -5x - 13y = -55 Eqn B
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3x + 2y = 4 Eqn A
-5x - 13y = -55 Eqn B
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15x + 10y = 20 Eqn A times 5
-15x - 39y = -165 Eqn B times 3
----------------------------------- Add
-29y = -145
y = 5
----
z = -2y+3
Sub for y & z in Eqn A or B to find x.