The circle graphic on this webpage link might help you understand how to answer the question. The key is that at 0 degrees sin is 0 and again at 180. But for cos at 0 is 1 and at 180 degrees is -1 and at key values in between they take on values of 1/2 and -1/2 and sqrt(2)/2 and sqrt(3)/2 [also plus and minus as you go around the circle]. for example at 150 degrees cos term is -sqrt(3)/2 and sin term is 1/2 at same 150 degrees. using these equivalent values you can reduce the first terms down to just constants of the values mentioned above and shown on graphic at this link: https://socratic.org/questions/how-do-you-evaluate-cos-1-1-2-without-a-calculator