Question 217226
{{{system( x-2y+3z=-1, 4x+5y+z=26, -x+y-2z=-1)}}}

From the last equation -x+y-2z=-1, you quickly get x = y-2z+1. 
substitute this in first two and simplify

first equation : (y-2z+1)-2y+3z=1 or -y+z=0
second equation: 4(y-2z+1)+5y+z=26, simplify this: 
*[invoke explain_simplification "4(y-2z+1)+5y+z=26" ]

so we get {{{ system( -y+z=0, 9y-7z=22) }}}

Solve it
*[invoke linear_substitution "y", "z", -1, 1, 0, 9, -7, 22 ]

Since y and z = 11, and x = y-2z+1, we get x = 11-22+1 = -10