Решите алгебр.слож: Система х+у=4              

Решите плииз..

                           Решение:

x+y=4             5x+2y=12            3x+7y=-1
-x+2y=2           4x+y=3               2x-3y=7
3y=6                5x+2y=12            6x+14y=-2
y=2                  8x+2y=6              6x-9y=21
x+2=4              -3x=6                   23y=-23
x=2                   x=-2                      y=-1
                        y=3-4x=3+8=11      2x=7+3y=7-3=4
                                                      x=2