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2010-01-06T17:53:27+01:00
A)
7y+12=2x-5
12y+7x-18=21

7y - 2x = -17 /*7
12y + 7x = 39 /*2

49y - 14x = -119
24y + 14x = 78
73y = -41
y = -41/73

2x = 17 + 7*-41/73
2x = 20 + 68/73
x = 10 + 68/146

b)
2(c+d)=1
c-d=c+d

c+d= 0,5
0 = 2d
d = 0
c = 0,5

c)
p+u-1=0
2p+u=0

u = 1 - p
u = -2p

-2p = 1 - p
-p = 1
p = -1

u = 1 + 1
u = 2
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2010-01-06T18:10:05+01:00
B) {2(c+d)=1
{ c-d=c+d
{2c+2d=1
{ c-c-d-d=0
{2c+2d=1
{ -2d=0
{2c=1/:2
c=½
d=0

2c+2d=1
1+0=1

c) {p+u-1=0
{2p+u=0
{p+u=1/×(-1)
{2p+u=0
{-p-u=-1
{2p+u=0
p=-1

2p+u=0
u=-2p
u=-2/×(-1)
u=2