Question:

A and B are two points on one bank of a straight river and C, D are two other points on the other bank... AB=a, $\angle CAD=α, \angle DAB=β, \angle CBA=γ$, then CD is equal to

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A and B are two points on one bank of a straight river and C, D are two other points on the other bank... AB=a, $\angle CAD=α, \angle DAB=β, \angle CBA=γ$, then CD is equal to
Updated On: Apr 15, 2026
  • $\frac{a \sin \beta \cdot \sin \gamma}{\sin \alpha \cdot \sin(\alpha+\beta+\gamma)}$
  • $\frac{a \sin \alpha \cdot \sin \gamma}{\sin \beta \cdot \sin(\alpha+\beta+\gamma)}$
  • $\frac{a \sin \alpha \cdot \sin \beta}{\sin \gamma \cdot \sin(\alpha+\beta+\gamma)}$
  • None of the above
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The Correct Option is B

Solution and Explanation

Step 1: Concept
Apply the Sine Rule in triangles $\Delta CAB$ and $\Delta CAD$.
Step 2: Analysis
In $\Delta CAB$, $\frac{AC}{\sin \gamma} = \frac{a}{\sin(\alpha+\beta+\gamma)}$, so $AC = \frac{a \sin \gamma}{\sin(\alpha+\beta+\gamma)}$.
Step 3: Evaluation
In $\Delta CAD$, $\frac{CD}{\sin \alpha} = \frac{AC}{\sin \beta}$.
Step 4: Conclusion
Substituting $AC$, we get $CD = \frac{a \sin \alpha \cdot \sin \gamma}{\sin \beta \cdot \sin(\alpha+\beta+\gamma)}$.
Final Answer: (b)
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