Question 1203438
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9x+18y-3z=18
9x-9y+15z=-18
9x+9y-2z=11
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Peform E1-E3 and E2-E3.


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9y-z=7
-18y+17z=-29
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Make 2*E1.

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18y-2z=14
-18y+17z=-29
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Perform E1+E2.


15z=-15


{{{z=-1}}}
With this, you can go back and find values for y and x.