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February 27th, 2013, 11:34 PM   #1
Doc
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Geometry problem

Hi,

I have struggled on this question, so your help is greatly appreciated.

Q: A(-2,-4) B(4,1) Using these coordinates write the equation of AB.

This is my working:

Gradient of AB= 5/6
y-1=5/6(x-4)
y-1= 5/6x-3 1/3 Then I multiply by 6 (LCM)

5x-6y=-14

However the correct answer is 5x-6y=15

How do you get this answer? Thanks for you help
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February 27th, 2013, 11:41 PM   #2
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Re: Geometry problem

I agree with you up to:



Multiply through by 6:







You can verify this is correct by substituting the coordinates from the given points into the equation.
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February 27th, 2013, 11:48 PM   #3
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Re: Geometry problem

Thanks very much. I used the other given coordinate and got the same answer. So is this just an error in my textbook?
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February 27th, 2013, 11:53 PM   #4
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Re: Geometry problem

Yes, you will occasionally find errors in your textbooks, but usually this if pretty rare. Errors are more common in earlier editions.
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