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.