MCQ
If $y = {\log _{\sin \,x}}\left( {\tan \,x} \right)$ , then ${\left( {\frac{{dy}}{{dx}}} \right)_{\pi /4}}$ is equal to
  • A
    $\frac{4}{{\ln \,2}}$
  • B
    $-4\ ln\ 2$
  • $\frac{{ - 4}}{{\ln \,2}}$
  • D
    $4\ ln\ 2$

Answer

Correct option: C.
$\frac{{ - 4}}{{\ln \,2}}$
c
$\mathrm{y}=\frac{\log \tan \mathrm{x}}{\log \sin \mathrm{x}}$

$\therefore \frac{\mathrm{dy}}{\mathrm{dx}}=\frac{(\log \sin \mathrm{x})\left(\frac{\sec ^{2} \mathrm{x}}{\tan \mathrm{x}}\right)-(\log \tan \mathrm{x})(\cot \mathrm{x})}{(\log \sin \mathrm{x})^{2}}$

or ${\left( {\frac{{dy}}{{dx}}} \right)_{\pi /4}} = \frac{{ - 4}}{{\log 2}}$ (On simplification)

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