Respostas

2013-11-24T20:58:42-02:00
3r + s = 7
 r - 2s = 0

s = 7 - 3r      isolar o S

r - 2(7 - 3r) =0
r - 14 + 6r = 0
7r = 14
r = 14/7
r = 2

achando S
s = 7 - 3r
s= 7 - 3 . 2
s= 7 - 6
s= 1