\[\sum\limits_{r=1}^{\infty }{{{\tan }^{-1}}\left( \frac{1}{1+r+{{r}^{2}}} \right)=....}\]

\[\sum\limits_{r=1}^{\infty }{{{\tan }^{-1}}\left( \frac{1}{1+r+{{r}^{

1.	\[\sum\limits_{r=1}^{\infty }{{{\tan }^{-1}}\left( \frac{1}{1+r+{{r}^{2}}} \right)=....}\]
A.	\[\frac{\pi }{2}\]
B.	\[\frac{\pi }{4}\]
C.	\[\frac{2\pi }{3}\]
D.	None
Answer» C. \[\frac{2\pi }{3}\]

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\[\sum\limits_{r=1}^{\infty }{{{\tan }^{-1}}\left( \frac{1}{1+r+{{r}^{2}}} \right)=....}\]

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