Resposta :
a) x+2y=9
2x-2y=9
3x = 18 ==> x = 6
x + 2y = 9 ==> 6 + 2y = 9 ==> 2y = 9-6 ==> 2y=3==>y=3/2
b) x+2y=9
-x+2y=9
4y =18 ==> y=18/4
x = 9- 2y ==>x = 9 - 2.18 ==> x = 36-36 ==> x = 0
4 4
2x-2y=9
3x = 18 ==> x = 6
x + 2y = 9 ==> 6 + 2y = 9 ==> 2y = 9-6 ==> 2y=3==>y=3/2
b) x+2y=9
-x+2y=9
4y =18 ==> y=18/4
x = 9- 2y ==>x = 9 - 2.18 ==> x = 36-36 ==> x = 0
4 4