Question:

$\displaystyle \int_{0}^{1} \left[\tan^{-1}\left(\frac{1}{1+x+x^2+x^3}\right) + \tan^{-1}(1+x+x^2+x^3)\right] dx$ is equal to:

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Look for inverse trig pair identities to simplify integrals instantly.
Updated On: Apr 24, 2026
  • $\frac{\pi}{4}$
  • $2\pi$
  • $\frac{\pi}{2}$
  • $1$
  • $4\pi$
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The Correct Option is C

Solution and Explanation

Concept:
• Identity: \[ \tan^{-1}x + \tan^{-1}\left(\frac{1}{x}\right) = \frac{\pi}{2}, \quad x>0 \]

Step 1:
Apply identity
\[ \tan^{-1}\left(\frac{1}{f(x)}\right) + \tan^{-1}(f(x)) = \frac{\pi}{2} \]

Step 2:
Simplify integrand
\[ = \frac{\pi}{2} \]

Step 3:
Integrate
\[ \int_{0}^{1} \frac{\pi}{2} dx = \frac{\pi}{2}(1-0) \] \[ = \frac{\pi}{2} \] Final Conclusion:
Option (C)
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