1. The problem statement, all variables and given/known data Find the co-ordinate of the centre of the following circle as a function of time: x2+y2 = C + 2 t x 2. Relevant equations 3. The attempt at a solution No idea..! It's part of a fluid dynamics problem, which I don't need to explain here, other than to say I plotted it on Mathematica and can see that the circle moves to the right at a rate of 't'. So the answer is : Centre of circle = (t, 0) as a function of time. But I don't know how to get to that answer. The only thing that I think might be helpful is to rearrange it into the form: x(x-2t)+y2 = C As this looks a little more like a circle and conforms a little bit to the (x-a)2+(y-b)2 = R2 idea. Thanks in advance!