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Algebra/help me please

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Expert: - 1/11/2010


Question
my textbook says to solve this system of linear equations with three variables using linear combinations.
the system is:

x+5y-z=16
3x-3y+2z=12
2x+4y+z=20

i have figured out what the value for y is by combining the first and the last equation and my answer for that was 3x+9y=36 and then i combined the first and second equation and got the answer 5x+7y=32 i then combined those two equations and got that y=3.5

that is as far as i can go because i do not understand what my next step is. will you please help me?

Answer
Well done!

Now you can plug the value of "y" in any of the two last equations you obtained. Note that they only have two variables: "x" and "y" ("z" is gone). So, if you plug in "y" you only have ONE variable ("x") and you can solve for it. Once you find "x" you can substitute "x" and y" in any of the 3 original equations to get "z".

Good luck,
David

Algebra

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David Montiel

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