MCQ
If $2\tan A = 3\tan B,$ then $\frac{{\sin 2B}}{{5 - \cos 2B}}$ is equal to
  • A
    $\tan A - \tan B$
  • $\tan (A - B)$
  • C
    $\tan (A + B)$
  • D
    $\tan (A + 2B)$

Answer

Correct option: B.
$\tan (A - B)$
b
(b) $2\tan {\rm A} = 3\tan B$

==> $\tan A = \frac{3}{2}\tan B = \frac{3}{2}t$,   [Let $\tan B = t$] 

==> $\sin 2B = \frac{{2t}}{{1 + {t^2}}},\cos 2B = \frac{{1 - {t^2}}}{{1 + {t^2}}}$ 

$\therefore$ $\frac{{\left( {\frac{{2t}}{{1 + {t^2}}}} \right)}}{{5 - \left( {\frac{{1 - {t^2}}}{{1 + {t^2}}}} \right)}}$

$ = \frac{{2t}}{{4 + 6{t^2}}} = \frac{t}{{2 + 3{t^2}}} = \tan (A - B)$.

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