Решите систему уравнений : 2(3х+2у)+9=4х+21 , 2х+10=3-(6х+5у).

 2(3х+2у)+9=4х+21

 2х+10=3-(6х+5у)

2(3х+2у)+9=4х+21

2х+10=3-6х-5у

8х=-5у-7

2(3х+2у)+9=4х+21

х=-0,625у-0,875

6х+4у+9=4х+21

х=-0,625у-0,875

2х + 4у=12

х=-0,625у-0,875

2(-0,625у-0,875) + 4у=12

х=-0,625у-0,875

-1,25у +4у =12+ 1,75

х=-0,625у-0,875

2,75у= 13,75

у= 5

х= -0,625*5-0,875

у=5

х=-4

ответ: (-4;5)