Posted by Wenny12 on Wednesday, April 20, 2011 at 12:18am.
need help with hw...
Use GaussJordan to solve
3x – 2y + z = 6
3x + y – z = 4
x + 2y – 2z = 8

Alg 2  Math  MathMate, Sunday, April 24, 2011 at 6:20am
Start by transcribing the equations to a 3x4 matrix
3 2 1 6
3 1 1 4
1 2 2 8
The first step is to reduce each column to zero (except the diagonal element and above) by linear combination of rows. I'll do the first one:
3 2 1 6
0 3 2 10 (row 2  row 1)
0 4 5 18 (3*row 3 + row 1)
Continue:
3 2 1 6
0 3 2 10
0 0 7 14 (4*row 2  3*row 3)
The last row can be simplified:
3 2 1 6
0 3 2 10
0 0 1 2
So z=2, substitute z=2 in row 2 to eliminate elements above the diagonal
3 2 0 4 (row 1  row 3)
0 3 0 6 (row 2 + 2*row 3)
0 0 1 2
Simplify row 2:
3 2 0 4
0 1 0 2 (row 2/3)
0 0 1 2
Now eliminate column 2 from row 1
3 0 0 0 (row 1 + 2*row 2)
0 1 0 2
0 0 1 2
So
x=0
y=2
z=2
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