MCQ
If $\tan A=2 \tan B+\cot B$, then $2 \tan (A-B)$ is equal to
  • A
    tan B
  • B
    2 tan B
  • cot B
  • D
    2 cot B

Answer

Correct option: C.
cot B
(C)
$2 \tan (A-B)=2\left(\frac{\tan A-\tan B}{1+\tan A \tan B}\right)$
$=2\left[\frac{2 \tan B+\cot B-\tan B}{1+(2 \tan B+\cot B) \tan B}\right]$
$\ldots[\because \tan A=2 \tan B+\cot B]$
$=2\left[\frac{\tan B+\cot B}{2\left(1+\tan ^2 B\right)}\right]$
$=\frac{\cot B \left(\tan ^2 B+1\right)}{1+\tan ^2 B}=\cot B$

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