Question

Решите системы, я не понимаю как)

Answer 1

1)
$left { {{3x + 2y = 8} atop {x-3y=21}} right.$⇒$left { {{3(21+3y)+2y=8} atop {x-3y=21}} right.$⇒$left { {{63 + 9y +2y = 8} atop {x-3y=21}} right.$⇒$left { {{11y =-55} atop {x-3y=21}} right.$⇒$left { {{y=-5} atop {x =6}} right.$