Take a look at triangle \(OPQ\) in this diagram. Explain why \(P\) has the coordinates given.
Imagine we move \(P\) by increasing \(\angle QOP\), whilst keeping \(PQ\) perpendicular to the \(x\)-axis.
How could \(P\) move if
the length of \(OP\) is fixed but \(Q\) can move along the \(x\)-axis as required?
\(Q\) remains fixed but the length of \(OP\) can change?
In each case, can you express the coordinates of \(P\) in terms of \(\angle QOP\) ?