Question

cos 3 b +cos 5 b + cos b/sin b +sin 5 b +sin 3 b
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Answer 1

Ответ:

ctg3b

Пошаговое объяснение:

sina+sinb=2sin((a+b)/2)cos((a-b)/2)

cosa+cosb=2cos((a+b)/2)cos((a-b)/2)

cosb+cos5b=2cos3bcos2b

sin5b+sinb=2sin3bcos2b

(cos3b+cos5b+cosb)/(sin5b+sin3b+sinb)=(2cos3bcos2b+cos3b)/(2sin3bcos2b+sin3b)=

=cos3b(2cos2b+1)/sin3b(2cos2b+1)=cos3b/sin3b=ctg3b