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Maths question

Posted on 2013-11-22
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Last Modified: 2013-11-23
I have a algebra question, the below problem already has the answer (4 & -2) but I need to know the x & y value AND the x and the y on both need to be the same value.. help lol

3x + 8y = 4
3x + 2y = -2
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Question by:1desman1
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LVL 85

Expert Comment

by:ozo
ID: 39670670
3x + 8y = 4
3x + 2y = -2
(3x-3x) + (8y-2y) = (4 - -2)
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Author Comment

by:1desman1
ID: 39670677
Thanks ozo!!

However, I probably didnt word it right

3x + 8y = 4
3x + 2y = -2

the x and both lines need to be the same value as does the y to get the answer... make sense?
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LVL 6

Expert Comment

by:ZamZ0
ID: 39670689
The 2 x values and the 2 y values must be the same but the x and the y could be different. So one way to solve this would be to take one of the equations and get it so one letter is on a side by itself.

3x+8y=4
8y=4-3x
y = (4-3x)/8

Now since you know what y is you can plug that into the second line.

From 3x+2y=-2 you get
3x+2*[(4-3x)/8]=-2
Then you can solve this algebraically to find that x is -4/3.

Now you can take that and plug it back into either one of the equations to be able to  solve for y.
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Expert Comment

by:akb
ID: 39670746
3x + 8y = 4
so: 3x = 4 -8y

3x + 2y = -2
so: 3x = -2 -2y

therefore:
4 - 8y = -2 -2y
so: 6 = 6y
so: y=1

therefore: 3x = -2 -2
so: 3x = -4
so: x = -4/3

RESULT: x=-4/3 and y=1
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Accepted Solution

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aburr earned 2000 total points
ID: 39670769
The complete statement of the problem might be

IF
3x + 8y = 4
AND
3x + 2y = -2,
what must be the value of x and y.

With the first equation only, x and y could be many different values but there are only certain values of x and y which fit BOTH equations.
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LVL 13

Expert Comment

by:akb
ID: 39672169
I'm confused by the accepted solution. That wasn't an answer to your question!
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LVL 85

Expert Comment

by:ozo
ID: 39672191
I guess the intended question wasn't the question some of us thought it was.
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