I did a past paper which had the following question:

Letp = sin40andq = cos110. Give your answers to the following in terms of p and/or q.

Write down an expression for

(i) sin140

(ii) cos70.

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.

Please explain!

Thanks