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This is a math question... i have the next problem ...

this is a math question... i have the next problem:

{X+Y=12
{2X+Y=-5

i dont find x and y can u help me?


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x+y = 12

x = 12 - y

 

2x + y = -5

2(12-y) + y = -5

24 - 2y + y = -5

24 -y = -5

y = 29

x = 12 - 29 = -17

Posted 2006-08-16T08:45:42Z
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Or you can use the elimination method, instead of the substitution method posted above:



(1). x   + y = 12
(2). 2x + y = -5

2(1) - (2): <-remember that you can change an equation as long as you do the same thing on both sides, it will still be balanced.

Basically, below is (2 times equation 1) minus (equation 2)
      2x + 2y = 24
-     2x + y   = -5
------------------------
(3).         y   = 29

Substitute y into either (1) or (2), here we will use (1)
x + 29 = 12
x         = 12 - 29
x         = -17

I like both methods, but since you're asking this question, I thought it'd be important for you to know both ways. I prefer this way in solving 3 equation systems with 2 unknowns. Or finding intersections of planes in 3-space, where you have 3 equations and 3 unknowns.
Posted 2006-08-16T14:00:19Z
Germanicus was invited by Yedda to answer this question.

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wow thanks! but its not what i mean :(
i forget  to write that what i need is a graphic answer, i know to answer it myself by this way (:

huge thanks again!!! 
Posted 2006-08-16T14:07:07Z
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Ah, this is simple too, you can use a graphing calculator, or use graphing paper and a pencil.



You have 2 eqations, they are linear equations. So you write them in terms of Y.

(1). x + y = 12
(2). 2x + y = -5

from (1): (3) y = -x + 12
from (2): (4) y = -2x - 5

Then you graph it. You'll get 2 lines intersecting somewhere. The intersection point's x and y coordinate are the answers to x and y.

The two lines should intersect at the point (-17, 29).

Reply back if you don't know how to graph.
Posted 2006-08-16T14:17:10Z
Germanicus was invited by Yedda to answer this question.

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This is known as a "system of linear equations" or "two variables and two equations."  With two letters and two different equations, a solution is easily found.  Remember, each equation is a line.  If two lines aren't parallel, then they intersect in a point.  The point is the solution.  Lets find the two coordinates of the point.

First, let's multiply the top equation by -2

     X+Y=12
   2X+Y=-5

becomes

   -2X-2Y=-24
    2X+Y=-5

Second, add the two equations together (2x and -2x are opposites)

        -y=-29

Third, solve for y

        y=29

Fourth, substitute into one of the two original equations and solve for x

       x+29=12

           x=-17

Have a great day.
Posted 2006-08-16T14:42:52Z
OrangeMath was invited by Yedda to answer this question.

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you can basicly take an ordinary paper for math (the one with the squares)ans plot both the equation on the same garph like this

 

the point the two line meet is the desired point.

 you can read it here

 
Posted 2006-08-17T10:26:05Z
yotama9 was invited by Yedda to answer this question.

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x+y=12

2x+y=-5 

 

x=12-y

 

2(12-y)+y=-5

 

24-2y+y= -5

-y=-29

y= 29

x= -17 
Posted 2006-08-19T09:36:33Z
U235 was invited by Yedda to answer this question.

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Germanicus you have suggested very good solution. it has solved that problem...
Posted 2009-10-19T08:43:41Z
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