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Question : 21 of 160
Marks:
+1,
-0
Solution:
cos‌+cos‌+cos‌+cos‌ =cos‌+cos‌+cos‌−1 =‌[2‌sin‌⋅cos‌+2‌cos‌⋅sin‌ +2‌cos‌‌sin‌]−1 =‌[sin(‌+‌)−sin(‌−‌)+sin(‌+‌) −sin(‌−‌)+sin(‌+‌)−sin(‌−‌)]−1 =‌[sin‌−sin‌+sin‌−sin‌ +sin‌π−sin‌]−1 =‌−1=−‌−1=‌
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