# Homework Help: Pivoting (Gaussian elimination)

1. Feb 23, 2017

### fonseh

1. The problem statement, all variables and given/known data

x1 + 2x2 = 9 ,
6x1 + 6x2 -8x3 = 1 ,
-3x2 +x3 = 0

Here's a question from my book . I'm asked to find the x1 , x2 and x3 by using the gaussian elimination with pivoting .

2. Relevant equations

3. The attempt at a solution

Pls refer to this thread for the lecturer's method

By using the lecturer's method ( circle out the max element in each column ) , I found that all the greatest element lies in 6x1+ 6x2 - 8x3 = 1 ...
So , how could all the largest element lies in the same row ?

Last edited: Feb 23, 2017
2. Feb 23, 2017

### BvU

Fate, coincidence, exercise composer's whim, anything. It happens. You just play along and swap rows 1 and 2 -- by the book .

3. Feb 23, 2017

### BvU

And if we are going to do much more of this, you should learn a bit of $\LaTeX$ instead of making photos. It's fun and pretty easy.
Code (LaTeX):

$$\begin{pmatrix} 1 & 2& 0 & 9 \\ 6 & 6 & -8 & 1 \\ 0 & -3 & 1 & 0 \end {pmatrix }   gives you$$\begin{pmatrix}
1 & 2& 0 & 9 \\
6 & 6 & -8 & 1 \\
0 & -3 & 1 & 0
\end {pmatrix} 

4. Feb 23, 2017

### fonseh

So
So , I cant use the lecturer's method to do this question ?

5. Feb 23, 2017