Question

Помогите пожалуйста!!!

Answer 1

$\left \{ {{x+2y =-5} \atop {x-y = 7}} \right.$
$\left \{ {{x+2y =-5} \atop {-x + y = -7}} \right.$ 
3y = -12
y=-4

x+2(-4) = -5
x=3

(x,y) = (3,-4)

$\left \{ {{3+2(-4)=-5} \atop {3-(-4) = 7}} \right.$ 
$\left \{ {{-5 = -5} \atop {7=7}} \right.$