Comprehension

Consider the following for the two (02) items that follow:
The top (M) of a tower is observed from three points P, Q and R lying in a horizontal straight line which passes directly along the foot (N) of the tower. The angles of elevations of M from P, Q and R are 30°, 45° and 60° respectively. Let PQ = a and QR = b

What is MN equal to?

This question was previously asked in
NDA-I (Mathematics) Official Paper (Held On: 13 Apr, 2025)
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  1. \( \left(\frac{3+\sqrt{3}}{2}\right)b\)
  2. \( \left(\frac{3-\sqrt{3}}{2}\right)b\)
  3. \( \left(\frac{3-\sqrt{3}}{4}\right)b\)
  4. \( \left(\frac{3+\sqrt{3}}{4}\right)b\)

Answer (Detailed Solution Below)

Option 1 : \( \left(\frac{3+\sqrt{3}}{2}\right)b\)
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Detailed Solution

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Calculation

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\( \tan(60^\circ) = \frac{h}{x} \Rightarrow h = \sqrt{3}x \)

\( \tan(45^\circ) = \frac{h}{b + x} \Rightarrow h = b + x \)

\( h = b + x \Rightarrow \sqrt{3}x = b + x \)

\( x = \frac{b(\sqrt{3} + 1)}{2} \)

\( h = MN = \sqrt{3}x = \left( \frac{3 + \sqrt{3}}{2} \right) b \)

Hence, the correct answer is Option 1.

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