1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Need help on this coordinate geomeotry question

  1. Jul 30, 2009 #1
    So heres how it goes.

    Find the coordinates of the centre and the radius of the circle
    x^2 + y^2 - 4x + 6y -12 =0

    a)If the circle cuts the x-axis at the points A and B , find the length of line segment AB.

    My question is , I have actually found 2 points , they are
    (-2,0) and (6,0)

    However , How do I know which point is A or which point is B?
    in the answer sheet , (-2,0) is A , but can anyone explain why?
    Why cant A be (6,0)?
  2. jcsd
  3. Jul 30, 2009 #2


    User Avatar
    Science Advisor

    Are you serious? It doesn't matter! You are not asked to find A and B separately you are asked to find the distance between A and B. And the distance "from A to B" is the same as the distance "from B to A".:smile:
  4. Jul 31, 2009 #3
    Yes , but right now Im asking why is A at (-2,0) and not at (6,0)?
    For A is used in the later part B , I dont have the question with me now , so I cant really describe the part B of the question...
  5. Jul 31, 2009 #4


    User Avatar
    Homework Helper
    Education Advisor
    Gold Member

    Recheck HallsOfIvy's answer again. The ordered pair values are important; not the name you gave the points. "A" and "B" are just names. The ordered pairs tell us WHERE each point is. You needed to find the ordered pairs, and you succeeded.
  6. Jul 31, 2009 #5
    Its probably because the -2,0 point lies to the left (occurs before) of the 6,0 point. There's no particular reason to it.
  7. Aug 1, 2009 #6


    User Avatar
    Science Advisor

    Who says that "A is at (-2, 0)"? If that information in in the question, it is because you are told that A is (-2, 0) and they want you to label the point (-2, 0) and use that later in the problem.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook