interchange first and last equation:

-x1 + 8x2 - 6x3 = 5

-x1 + 7x2 – 5x3 = 4

0 + 4x2 – 3x3 = 3

Subtract equation 1 from 2:

-x1 + 8x2 - 6x3 = 5

0 - 1x2 + x3 = -1

0 + 4x2 – 3x3 = 3

Add 4 times the second to the last:

-x1 + 8x2 - 6x3 = 5

0 - 1x2 + x3 = -1

0 + 0 + 1x3 = -1

Now start the back substitution with x3=-1, put this into the second to find x2, etc..

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