MCQ
The value of $\tan\text{x}\tan\Big(\frac{\pi}{3}-\text{x}\Big)\tan\Big(\frac{\pi}{3}+\text{x}\Big)$ is:
  • A
    $\cot3\text{x}$
  • B
    $2\cot3\text{x}$
  • $\tan3\text{x}$
  • D
    $3\tan3\text{x}$

Answer

Correct option: C.
$\tan3\text{x}$
$\frac{\pi}{3}=60^\circ$
$\tan​​\text{x}\tan(60^\circ-\text{x})\tan(60^\circ+\text{x})\\=\tan\text{x}\times\frac{\tan60^\circ-\tan\text{x}}{1+\tan60^\circ\tan\text{x}}\times\frac{\tan60^\circ+\tan\text{x}}{1-\tan60^\circ\tan\text{x}}$
$=\tan\text{x}\times\frac{\sqrt{3}-\tan\text{x}}{1+\sqrt{3\tan\text{x}}}\times\frac{\sqrt{3}+\tan\text{x}}{1-\sqrt{3}\tan\text{x}}$
$=\frac{\tan\text{x}(3-\tan^2\text{x})}{1-3\tan^2\text{x}}$
$=\frac{3\tan\text{x}-\tan^3\text{x}}{1-3\tan^2\text{x}}$
$=\tan3\text{x}$

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