Solve the system using augmented matrix. Show your work.
I just don't know what to do!
Write that as a matrix by dropping the letters
and putting vertical line instead of equal signs:
The idea is to get three zeros in the three positions
in the lower left corner of the matrix, where the elements
I've colored red are:
To get a 0 where the red 2 is, multiply R3
by 2 and add it to 1 times R2, and put it in place of the
present R2. That's written as
2R1+1R2->R2
To make it easy, write the multipliers to the left of the two
rows you're working with; that is, put a 2 by R1 and a 1 by R2
We are going to change only R2. Although R3 gets multiplied
by 2 we are going to just do that mentally and add it to R2, but
not really change R3.
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To get a 0 where the lower left red -1 is, multiply R1
by 1 and add it to 5 times R3. That's written as
1R1+5R3->R3
Write the multipliers to the left of the two rows you're
working with; that is, put a 1 by R1 and a 5 by R3
We are going to change only R3.
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To get a 0 where the remaining red -1 is, multiply R2
by 1 and add it to -4 times R3. That's written as
1R2-4R3->R3
Write the multipliers to the left of the two
rows you're working with; that is, put a +1 by R2 and a -4 by R3
We are going to change only R3.
Now that we have 0's in the three positions in the
lower left corner of the matrix, we change the matrix
back to equations:
Solve the third equation for z:
Substitute 3 for z in the middle equation:
Substitute 3 for z and 1 for y in the top equation:
So the solution is 
Edwin
