February 27th, 2013, 11:34 PM  #1 
Member Joined: Aug 2012 Posts: 71 Thanks: 1  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 y1=5/6(x4) y1= 5/6x3 1/3 Then I multiply by 6 (LCM) 5x6y=14 However the correct answer is 5x6y=15 How do you get this answer? Thanks for you help 
February 27th, 2013, 11:41 PM  #2 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 521 Math Focus: Calculus/ODEs  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. 
February 27th, 2013, 11:48 PM  #3 
Member Joined: Aug 2012 Posts: 71 Thanks: 1  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?

February 27th, 2013, 11:53 PM  #4 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,211 Thanks: 521 Math Focus: Calculus/ODEs  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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