Question

{x + y = 1,
{2x + y = -1



СПОСІБ ПІДСТОНОВКИ​

Answer 1

крч
{x=1-y
{2x+y= -1
{x=1-y
{2(1-y)+y= -1
{x=1-y
{2-2y+y=-1
{x=1-y
{2-1y=-1
{x=1-y
{-1y=-1-2=-3
{x=1-y
{y=-3/-1
{x=1-y
{y=3
{x=1-3=-2
{y=3
{x=-2

Answer 2

$\displaystyle \left \{ {{x+y=1} \atop {2x+y=-1}} \right. \\\\\left \{ {{y=1-x} \atop {2x+y=-1}} \right. \\\\2x+1-x=-1\\x=-2\\y=1-(-2)\\y=3\\(x,y)=(-2,3)$