Question 1026763
<pre>
y + 3z = 7 + 4x
2y + x = 1 - 5z
6x - 9 = 2y + 3z

First arrange terms in alphabet order on the left
and constant terms on the right, like this:
{{{matrix(3,9,

-4x,""+"",1y,""+"",3z,"",""="","", 7, 
 1x,""+"",2y,""+"",5z,"",""="","", 1, 
6x,""-"",2y,""-"",3z,"",""="","", 9)}}}

Put all the coefficients in a 3x3 matrix,
multiplied by a 3x1 matrix of unknowns or 
variables, and set that equal to the 3x1
matrix of constants on the right:

{{{(matrix(3,3,-4,1,3,1,2,5,6,2,-3))*(matrix(3,1,x,y,z))}}}{{{""=""}}}{{{(matrix(3,1,7,1,9))}}}

That's {{{A*X}}}{{{""=""}}}{{{B}}} form

because {{{A}}}{{{""=""}}}{{{(matrix(3,3,-4,1,3,1,2,5,6,2,-3))}}}, 
{{{X}}}{{{""=""}}}{{{(matrix(3,1,x,y,z))}}}, 
{{{B}}}{{{""=""}}}{{{(matrix(3,1,7,1,9))}}}

Edwin</pre>