Part (c)(ii)
- Author:
- Alexander Wong
R can be moved. Now it is on the circle through P, Q and S. So you can use (b)'s results for R.
In (c)(i), you did something with O, A and B. You know that OB is the diameter of circle OAB. Hence the whole situation reduces to: Show that C (the stereographic projection of R) lies on this circle OAB.