MCQ
Evaluate: $\int \tan x \tan 2 x \tan 3 x d x$
  • A
    $\frac{1}{3} \log |\sec 3 x|-\log |\sec x|+C$
  • B
    $\log |\sec 3 x|-\frac{1}{2} \log |\sec 2 x|+C$
  • C
    $\log |\sec x|-\frac{1}{2} \log |\sec 3 x|+\frac{1}{2} \log |\sec 2 x|+C$
  • $\frac{1}{3} \log |\sec 3 x|-\frac{1}{2} \log |\sec 2 x|-\log |\sec x|+C$

Answer

Correct option: D.
$\frac{1}{3} \log |\sec 3 x|-\frac{1}{2} \log |\sec 2 x|-\log |\sec x|+C$
Let $I=\int \tan x \tan 2 x \tan 3 x d x$
$\text { Since, } \tan 3 x=\tan (2 x+x)=\frac{\tan 2 x+\tan x}{1-\tan x \tan 2 x}$
$\Rightarrow \tan x \tan 2 x \tan 3 x=\tan 3 x-\tan 2 x-\tan x ...(i)$
$\therefore I=\int(\tan 3 x-\tan 2 x-\tan x) d x \ ($From $(i))$
$=\frac{1}{3} \log |\sec 3 x|-\frac{1}{2} \log |\sec 2 x|-\log |\sec x|+C$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free