Question 1139579: solve with substitution
x+y+z=15
2X-y+3z=-5
-x-y+z+-7
Answer by Alan3354(69443)   (Show Source):
You can put this solution on YOUR website! solve with substitution
x+y+z=15
2X-y+3z=-5
-x-y+z+-7
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The 3rd row has no equal sign.
I'll assume you meant:
solve with substitution
x+y+z=15
2X-y+3z=-5
-x-y+z = -7
--------------
x + y + z = 15
2x -y +3z = -5
-x - y + z = -7
=====================
Add eqns 1 & 3
2z = 8
z = 4
==============
Sub for z in eqns 1 & 2
---
x + y + 4 = 15 ------------- Eqn A
2x -y +12 = -5
----------------------- Add
3x + 16 = 10
3x = -6
x = -2
----------------
Sub for x in eqn A
x + y + 4 = 15
-2 + y + 4 = 15
y = 13
(-2,13,4)
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