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2010-01-17T14:16:23+01:00
A)
½x + ⅓y = 18|*2
½x=⅔y

x+2/3y=36
½x=⅔y

x=36-2/3y
1/2(36-2/3y)=2/3y

x=36-2/3y
18-2/6y=2/3y

x=36-2/3y
-2/6y-2/3y=-18

x=36-2/3y
-y=-18|:(-1)

x=36-2/3y
y=18

x=36-2/3*18
y=18

x=24
y=18

b)
x-150=y+150
¼x=y

x-y=300
1/4x=y

-y=300-x|:(-1)
1/4x=y

y=-300+x
1/4x=-300+x

y=-300+x
1/4x-x=-300

y=-300+x
-3/4x=-300|:(-3/4)

y=-300+x
x=400

y=-300+400
x=400

y=100
x=400

c)
x+y=45
x-y=25
2x=70|:2
x=35

35+y=45
y=45-35
y=10

x=35
y=10


d)
x=y+5
x-1=2(y-1)

x=y+5
x-1=2y-2

x=y+5
y+5-1=2y-2

x=y+5
y-2y=-2-5+1

x=y+5
-y=-6|:(-1)

x=y+5
y=6

x=6+5
y=6

x=11
y=6