Determinante del sistema:
     3    -  4
                   D = (3)(-5) - (8)(-4) = - 15 + 24 = 9
     8     - 5
Dx
     13     - 4
                     Dx = (13)(-5) - (-5)(-4) = - 65 - 20 = - 85
     -5     - 5
                    Dx/D = x = - 85/9
Dy
     3       13
                     Dy = (3)(-5) - (13)(8) = - 15 - 104 = - 119
     8       - 5
                     Dy/D = y = - 119/9