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Question : 23 of 160
Marks:
+1,
-0
Solution:
Given,
A+B+C=4S⇒‌=2S To find :
cos(2S−A)+cos(2S−B)−cos(2S−C) −cos‌2‌S cos(‌−A)+cos(‌−B) −cos(‌−C)−cos(‌) =cos(‌)+cos(‌) −cos(‌)−cos(‌) =cos(‌)−cos(‌) +cos(‌)−cos(‌) =2‌sin(‌)⋅sin(‌)+2‌sin(‌)⋅sin(‌) =2‌sin(‌){sin(‌)+sin(‌)} {| ∵cos‌C−cos‌D=2‌sin‌⋅sin‌ |
| ‌ and ‌sin‌C+sin‌D=2‌sin‌⋅cos‌ |
} =sin(‌){2‌sin(‌)⋅cos(‌)} =4‌sin(‌)‌sin(‌)⋅cos(‌)
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