Respostas

2014-05-24T23:26:31-03:00
A)
3x+y=9
y=9-3x
Substituindo:
2x + 3(9-3x) = 13
2x + 27 - 9x = 13
-7x = 13 - 27
-7x = -14
x = 14/7
x = 2

y = 9-3(2)
y = 9-6 = 3

b)
x+y =8
y = 8-x
2x - (8-x) = 1
2x - 8 +x = 1
3x = 1+8
3x = 9
x = 9/3 = 3
y = 8-3
y = 5

c)
2x+3y=13
3y = 13-2x
y = (13-2x)/3
3x - 5y = 10
3x - 5((13-2x)/3) = 10
3x - (65 - 10x)/3 = 10
tirando o mmc
9x - 65 + 10x = 30
19x = 30+65
x = 95/19
x = 5

2x + 3(5) = 13
2x +15 = 13
2x = 13 - 15
2x = -2
x = -2/2 = -1
x = 149