Respostas

2013-08-15T21:23:26-03:00
A)  \left \{ {x+y=7} \atop {2x-y=-1}} \right.
y= 7 - x
2x - (7-x) = -1 
2x - 7 - x = -1
x - 7 = -1
x = -1 + 7 =6

b)  \left \{ {{x+2y=5} \atop {2x+y=-2}} \right.
x =  5 - 2y
2(5-2y) + y = -2
10 - 4y + y = -2
10 - 3y = -2
-3y = -2 + 10
-3y = 8   .(-1)
3y = -8
y = -8/3
6 4 6
2013-08-15T22:29:42-03:00
3X= 6
X=6/3
X=2

(pega a primeira questao)
x+y=7
2+y=7
y=7-2
y= 5

S{2;5}
1 5 1