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August 2, 2015

Homework Help: Math

Posted by Linda on Tuesday, November 1, 2011 at 2:19am.

Solve the system using any algebraic method.
2x - 2y + z = 3
5y - z = -31
x + 3y + 2z = -21
______________________
The answer I got for this is ( -26, 6,67) but I know its wrong and I don't know why. Help please >< my work is at the bottom

I used substitution method changed 5y-z=-31 to z=5y+31 then I:
Plugged it in the first equation=
2x-2y+5y+31=3 -> 2x+3y+31=3 -> 2x+3y=-28 is my new 1st equation...
Plugged in z=5y+31 to equation 3 =
x+3y+2(5y+31)=-21 -> x+3y+10y+62=-21 -> x+13y+62=-21 -> x+13y=-83 is my new 2nd equation.
2(=13y=82)+3y=-28 -> -26-166+3y=-28 -> -23y=138 - > y=6
2x+3(6)=-28 -> 2x+18=-28 -> 2x=-46 -> x=-23
2(-26)-2*6)+z=3 -> -52-12+z=3 -> -64+z=3 -> z=67

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