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Question : 21 of 160
Marks:
+1,
-0
Solution:
Given,
‌cos3‌⋅cos‌+sin‌3‌⋅sin‌‌‌‌ Using ‌‌=‌−‌‌⇒cos‌=sin‌‌‌ and ‌sin‌‌=cos‌‌⇒cos3‌⋅sin‌‌+sin‌3‌⋅cos‌‌‌‌=sin‌‌⋅cos‌(cos2‌+sin‌2‌)‌‌‌=‌2sin‌‌‌cos‌‌‌‌=‌sin‌‌=‌
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