# Math Help - Finding a sum of sines and cosines.

1. ## Finding a sum of sines and cosines.

Find: $S=4. sin^{2}10 + 4 sin^{2}50.cos20 + cos80$

2. Originally Posted by arm
Find: $S=4. sin^{2}10 + 4 sin^{2}50.cos20 + cos80$
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