Click and drag the red points to see what happens.

You can use the dynamic geometry applet to move the points $C$, $P$, $Q$, $R$ and $S$ and observe the changing angles.

You are given a variable point $C$ inside a circle and any two chords $PCS$ and $QCR$ through $C$.

Investigate the angle $RCS$.

State and prove a generalisation of the theorem about the angle at the centre of a circle being twice the angle at the circumference subtended on the same arc.