I was more thinking along the line of a circle being defined as

```
p(t)=o+xsin(t)+ycos(t)
```

where p, o, x and y are 3-tuples (the origin, X- and Y-axis of the circle plane, respectively)

Then you want to compute the equality of two circles

```
p(t) = o1+x1*sin(t)+y1*cos(t)
q(u) = o2+x2*sin(u)+y2*cos(u)
p(t) = q(u)
solve for t and u
```