Question

x+y=-1
x-y=-2         sistem de ecuatii

Answer 1

x + y = - 1
x - y = - 2
adunam cele 2 ecuatii
2x  /  = - 3
x = - 3/2
-3/2 + y = - 1
y = 3/2 - 1
aducem la acelasi numitor
2y = 3 - 2
y = 1/2

Answer 2

$\left \{ {{x+y=-1} \atop {x-y=-2}} \right. \\ .................. \\ 2x / =-3 => \ \ \boxed{ x=-\frac{3}{2}} \\ \\ -\frac{3}{2}+y^{(2}=-1^{(2} \\ \\ -3+2y=-2 \\ \\ 2y=-2+3 \\\\ 2y=1 => \boxed{y=\frac{1}{2}}$