First slide
Trigonometric transformations
Question

sin10+sin20+sin30+sin40cos10+cos20+cos30+cos40=

Moderate
Solution

We have sinα+sinα+d+.....sinα+n1dcosα+cosα+d+.....cosα+n1d=sinα+α+n1d2cosα+α+n1d2

sin1+sin2+sin3+sin4cos1+cos2+cos3+cos4=sin1+42ocos1+42o=tan52o

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