Question 192037
x - 4y + z= 9
0 + 3y -2z= -7
-x + 0  +z= 0 
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Add the 1st row to the 3rd to get:
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x - 4y + z = 9
0 + 3y -2z =-7
0 + -4y +2z= 9 
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Add the 2nd row to the 3rd row to get:
x - 4y + z = 9
0 + 3y -2z =-7
0 + -y + 0=  2 
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The 3rd row tells you y = -2
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Substitute into the 2nd row to solve for "z":
3(-2) - 2z = -7
-6 -2z = -7
-2z = -1
z = 1/2
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Substitute into the 1st row to solve for "x":
x - 4y + z = 9
x -4(-2) + (1/2) = 9
x + 8 1/2 = 9
x = 1/2
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Cheers,
Stan H.