question_answer

If \[{{\cos }^{-1}}\,\,\left( \frac{1}{x} \right)=\theta ,\]then \[\tan \theta =\]

A)  \[\frac{1}{\sqrt{{{x}^{2}}-1}}\]                      

B)  \[\sqrt{{{x}^{2}}-1}\]

C)  \[\sqrt{1-{{x}^{2}}}\]             

D)  \[\sqrt{{{x}^{2}}-1}\]

E)  None of these