A couple of cases in engineering that give rise to simultaneous linear equations.
-2x1 + (2+5+4+1)x2 – 4x3 – x4 = 0
-6x1 – 4x2 + (4+9+6)x3 – 9x4 = 0
-x2 – 9x3 + (9+1+11)x4 = 0