Ответы и объяснения

2013-11-24T13:23:40+04:00
1.x+y=7 |*3                                         4.4+y=7
x-3y=-5                                                  y=3

2.3x+3y=21                                       5.(4;3)- решение системы
x-3y=-5

3.4x=16 | : 4
x=4