A = [18 -3 0 0.0; 2 -13 1 10 ; 0 7 -17 10 ; 0 28 4 -39 ] b = [500.0; 0; 0; 0] v = A \b
4-element Array{Float64,1}: 30.2876 15.0592 13.3672 12.1827
A = [3.0 6 9; 2 5 -2; 1 3 -1] b = [39; 3; 2.0] A \ b
3-element Array{Float64,1}: 2.0 1.0 3.0