Hello user_5Two things you need to know first:

- the co-ordinates of any point, P, on the unit circle are where is the angle through which OP has rotated anticlockwise from the positive -axis.

So, in the diagram, and and so

OK, so how do we find ?

- Look at the point on the unit circle where the angle is .

- Work out its coordinates by reflecting the first point in the -axis.

- Now write down and

- Divide as I did above to give

Do in exactly the same way.

Can you complete it now?

Grandad