question_answer

If \[{{\tan }^{-1}}x+{{\tan }^{-1}}y+{{\tan }^{-1}}z=\pi ,\] then \[\frac{1}{xy}+\frac{1}{yz}+\frac{1}{zx}=\]

A)  \[0\]                            

B)  \[1\]

C)  \[\frac{1}{xyz}\]                                  

D)  \[xyz\]

E)  None of these