{2x+y=3 {x-y=9

2x + y = 3 x - y = 9 dodajemy stronami 2x + x + y - y = 3 + 9 3x = 12 x = 4 x - y = 9 4 - y = 9 - y = 9 - 4 - y = 5 y = -5 x = 4 y = -5

{2x+y=3 {x-y=9 {y=3-2x {x-(3-2x)=9 {y=3-2x {x-3+2x=9 {y=3-2x {3x=12/:3 x=4 {x=4 {y=-5