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**schwebba****Member**- Registered: 2005-07-25
- Posts: 2

I got some trouble with finding out how to calculate this..

Question: Where do these lines cross eachother x + 3y +3=0 and x - 3y +2 =0

First i tried to solve y and got this far

y = -1/3x - 1 = 1/3x+2/3 (divided all with 3)

but im not even sure if that is right. can anyone please explain how i can do this?

*Last edited by schwebba (2005-07-25 12:32:03)*

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**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 18,660

Solving the two equations, you get

x = -5/2, y = -1/6

Hence, the two lines cross at

(-5/2, -1/6)

How the two equations are solved:-

First equation can be written as x+3y = -3

The second equation can be written as x - 3y = -2

Adding the two, we get 2x = -5, or x = -5/2

Substituting this value in equation (1) -5/2 + 3y = -3

3y = -3 + 5/2

3y = -1/2

y = -1/6

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,582

Neatly solved!

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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**schwebba****Member**- Registered: 2005-07-25
- Posts: 2

wow thanks i think i get it now. you sure cleared things up a bit

gonna practise some more on this..

thanks a lot for that nice solution

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,582

And for all those avid graphers out there, I have a little tool to figure out lines from points here: http://www.mathsisfun.com/straight-line … ulate.html

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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