Question:

If $\tan \alpha = \dfrac{5}{6}$ and $\tan \beta = \dfrac{1}{11}$, where $0<\alpha,\beta<\dfrac{\pi}{2}$ then $\alpha + \beta =$:

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If $\tan(\theta)=1$, then $\theta = \frac{\pi}{4}$ in first quadrant.
Updated On: Apr 24, 2026
  • $\frac{\pi}{6}$
  • $\frac{\pi}{2}$
  • $\frac{\pi}{3}$
  • $\frac{\pi}{4}$
  • $\frac{2\pi}{3}$
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The Correct Option is D

Solution and Explanation

Concept:
• $\tan(\alpha + \beta) = \dfrac{\tan\alpha + \tan\beta}{1 - \tan\alpha \tan\beta}$

Step 1:
Apply formula
\[ \tan(\alpha + \beta) = \frac{\frac{5}{6} + \frac{1}{11}}{1 - \frac{5}{6}\cdot\frac{1}{11}} \]

Step 2:
Simplify numerator
\[ \frac{5}{6} + \frac{1}{11} = \frac{55 + 6}{66} = \frac{61}{66} \]

Step 3:
Simplify denominator
\[ 1 - \frac{5}{66} = \frac{61}{66} \]

Step 4:
Compute value
\[ \tan(\alpha + \beta) = \frac{61/66}{61/66} = 1 \]

Step 5:
Find angle
\[ \alpha + \beta = \frac{\pi}{4} \] Final Conclusion:
\[ = \frac{\pi}{4} \]
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