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!

Homework Help: Equation of a circle

  1. Dec 11, 2008 #1
    1. The problem statement, all variables and given/known data
    This is from one of the online textbooks recommended on the site, but it only has selected answers and this one's not included.
    A circle passes through the points (0,0), (0,1) and (2,0). What is it's equation.

    2. Relevant equations
    I think the form is the (y1-y0)2+(x1-x0)2=r2.
    So I got (y-1/2)2+(x-1)2=r2. Since the radius has to extend to each of these points from the centre, I think this does it. Apologies for the hurried post, I will elaborate as soon as possible if necessary, but I think this is enough information (my computrers broke so I have to use a library one!... and there's only five minutes left!).
    Is this answer right? Or have I misunderstood?!
    Thanks in advance.
  2. jcsd
  3. Dec 11, 2008 #2


    User Avatar
    Science Advisor

    Okay, so you say you have calculated the center of the circle to be (1, 1/2)? How did you get that? (I can think of three ways. I suspect you used the simplest.) Assuming that is correct, all you need to do is determine r: Find the distance from (1, 1/2) to any one of those points (or try all three as a check).
  4. Dec 12, 2008 #3
    Sorry, I thought about it last night after I posted and realised I could put in r. I got [tex] \frac{\sqrt{5}}{2}[/tex]. I tried it and it works. I think...?
    You mentioned three ways of finding the equation, could you elaborate as I would greatly appreciate it. I based it on that two of the points share the y-axis and two of the points share the x-axis, and deduced that the radius has to extend to all these points. (thanks for pointing out that I probably used the simplest method, very encouraging...:redface:)
    As always, thankyou for the response, and thanks in advance.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook