Question

Решите системы, я не понимаю как)

Answer 1

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