# Thread: 1.1.10 matrix simulatanious 5x4

1. ## 1.1.10 matrix simulatanious 5x4

$$\left[\begin{array}{rrrrr} 1& \,3& \,0& \,-2& \,-7\\ 0& 1& 0& 3& 6\\ 0& 0& 1& 0& 2\\ 0& 0& 0& 1& -2 \end{array}\right] %\stackrel{a}{\sim}$$
$$\begin{array}{rrrrrrl}\displaystyle x_1& +3x_2& & -2x_4& =&-7&\qquad(1)\\ & x_2& & +3x_4& =& 6&\qquad(2)\\ & & x_3& & =& 2&\qquad(3)\\ & & & x_4& =&-2&\qquad(4)\\ \end{array}$$
$\textit{$x_4=-2$so then}$
$$\begin{array}{rrrrrrll}\displaystyle %x_1& +3x_2& & -2(-2)& =&-7 &\qquad(5)\\ & x_2& & +3(-2)& =& 6 &\qquad(6)\\ \end{array}$$
$\textit{From (2)$x_2=6+6=12$}\\$
$\textit{Now we have$x_2=12, \,x_4=-2$}$
$$\begin{array}{rrrrrrl}\displaystyle x_1& +3(12)& & -2(-2)& =&-7 &\qquad(7)\\ x_1& +36& & +4& =&-7 &\qquad(8)\\ &&&&x_1&=?? \end{array}$$

ok I ran this on W|A and it returned $\displaystyle x_1=-35,x_2=8,x_3=2,x_4=-2,$

but can"t find the errors

2. ## Re: 1.1.10 matrix simulatanious 5x4

Originally Posted by bigwave
$$\left[\begin{array}{rrrrr} 1& \,3& \,0& \,-2& \,-7\\ 0& 1& 0& 3& 6\\ 0& 0& 1& 0& 2\\ 0& 0& 0& 1& -2 \end{array}\right] %\stackrel{a}{\sim}$$
$$\begin{array}{rrrrrrl}\displaystyle x_1& +3x_2& & -2x_4& =&-7&\qquad(1)\\ & x_2& & +3x_4& =& 6&\qquad(2)\\ & & x_3& & =& 2&\qquad(3)\\ & & & x_4& =&-2&\qquad(4)\\ \end{array}$$
$\textit{$x_4=-2$so then}$
$$\begin{array}{rrrrrrll}\displaystyle %x_1& +3x_2& & -2(-2)& =&-7 &\qquad(5)\\ & x_2& & +3(-2)& =& 6 &\qquad(6)\\ \end{array}$$
$\textit{From (2)$x_2=6+6=12$}\\$
$\textit{Now we have$x_2=12, \,x_4=-2$}$
$$\begin{array}{rrrrrrl}\displaystyle x_1& +3(12)& & -2(-2)& =&-7 &\qquad(7)\\ x_1& +36& & +4& =&-7 &\qquad(8)\\ &&&&x_1&=?? \end{array}$$

ok I ran this on W|A and it returned $\displaystyle x_1=-35,x_2=8,x_3=2,x_4=-2,$

but can"t find the errors
using the matrix written above Mathematica returns

$\{-47,12,2,-2\}$

you entered it into WA incorrectly.

3. ## Re: 1.1.10 matrix simulatanious 5x4

ok I saw the error

never ever used Mathematica!

btw where do you set the thread as "solved"