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The sum of the infinite series cot – 1 7 4       + cot – 1 19 4       + cot – 1 39 4       + cot – 1 67 4 + ... is :

1. –1 1 cot 2 2        
2. –1 1 tan 2 2        
3. –1 1 tan 2 2        
4. –1 1 cot 2 2        

Correct answer: –1 1 tan 2 2        

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