Question

Реши систему уравнений

Answer 1

$x - y = 3 \\ - 2x - y = 0 \\ \\ x - y = 3 \\ 2x + y = 0 \\ \\ 3x = 3 \\ y = -2x \\ \\ x = 1 \\ y = - 2$

Answer 2

x-y=3
-2x-y=0

x=3+y
-2x-y=0

-2(3+y)-y=0
y=-2
-2x-(-2)=0
x=1
(x,y)=(1,-2)
1-(-2)=3
-2*1-(-2)=0

3=3
0=0

ответ: (x,y)=(1,-2).