MCQ
The value of $\tan\bigg[\frac{1}{2}\cos^{-1}\Big(\frac{2}{3}\Big)\bigg]:$
  • $ \frac { 1 }{ \sqrt { 5 } }$
  • B
    $ \frac { 1 }{ \sqrt { 7 } }$
  • C
    $ \frac { 1 }{ \sqrt { 8 } }$
  • D
    $ \frac { 1 }{ \sqrt { 9 } }$

Answer

Correct option: A.
$ \frac { 1 }{ \sqrt { 5 } }$
We have, $\tan\bigg[\frac{1}{2}\cos^{-1}\Big(\frac{2}{3}\Big)\bigg]$
Put $ \cos ^{ -1 }{ \frac { 2 }{ 3 } } =θ$
$ \Rightarrow \cos { \theta } =\frac { 2 }{ 3 }$
$\therefore\tan\bigg[\frac{1}{2}\cos^{-1}\Big(\frac{2}{3}\Big)\bigg]$
$ \therefore \ \tan\frac{\theta}{2}=\sqrt {\frac {1-\cos {\theta}}{1+\cos{\theta }}}$
$=\sqrt {\frac {1-\frac{2}{3} }{1+{\frac{ 2}{3}}}}​​$
$=\sqrt { \frac { \frac{ 1 }{ 3 } }{ \frac{5}{3} } } $
$=\frac { 1 }{ \sqrt { 5 } }$

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