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Question : 127 of 180
Marks:
+1,
-0
Solution:
‌‌ We have, ‌cot−1(21)+cot−1(13)+cot−1(−8)‌=tan−1(‌)+tan−1(‌)+cot−1(−8)‌=tan−1(‌)+cot−1(−8)‌=tan−1(‌)+(π−cot−18) [∵cot−1(−x)=π−cot−1x]‌=tan−1(‌)−cot−18+π‌=tan−1(‌)−tan−1(‌)+π=π−cot−1x]
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