MCQ
If $\alpha  = {\cos ^{ - 1}}\,\left( {\frac{3}{5}} \right),\beta  = {\tan ^{ - 1}}\,\left( {\frac{1}{3}} \right)$, where  $0 < \alpha ,\beta  < \frac{\pi }{2}$, then $\alpha  - \beta $ is equal to
  • ${\sin ^{ - 1}}\,\left( {\frac{9}{{5\sqrt {10} }}} \right)$
  • B
    ${\cos ^{ - 1}}\,\left( {\frac{9}{{5\sqrt {10} }}} \right)$
  • C
    ${\tan ^{ - 1}}\,\left( {\frac{9}{{5\sqrt {10} }}} \right)$
  • D
    ${\tan ^{ - 1}}\,\left( {\frac{9}{{14}}} \right)$

Answer

Correct option: A.
${\sin ^{ - 1}}\,\left( {\frac{9}{{5\sqrt {10} }}} \right)$
a
$\cos \alpha  = \frac{3}{5},\tan \beta \frac{1}{3}$

$ \Rightarrow \tan \alpha  = \frac{4}{3}$

$ \Rightarrow \tan \left( {\alpha  - \beta } \right) = \frac{{\frac{4}{3} - \frac{1}{3}}}{{1 + \frac{4}{3},\frac{1}{3}}} = \frac{9}{{13}}$

$ \Rightarrow \sin \left( {\alpha  - \beta } \right) = \frac{9}{{5\sqrt {10} }}$

$ \Rightarrow \alpha  - \beta  = {\sin ^{ - 1}}\left( {\frac{9}{{5\sqrt {10} }}} \right)$

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