I did a past paper which had the following question:
Let p = sin40 and q = cos110. Give your answers to the following in terms of p and/or q.
Write down an expression for
Apparently the answer for (i) is p = sin140 and for (ii) cos70 = -q
I do not understand why is that the answer. Is it anything to do with the CAST unit circle idea? If it is then it would not make sense for cos.