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At a point on level ground, the tangent of the angle of elevation of the top of a tower is found to be \(\frac{5}{6}\). On walking 70 m towards the tower, the tangent of the angle of elevation of the top of the tower is found to be \(\frac{9}{2}\). What is the height of the tower ?

This question was previously asked in
CDS 1 2026 Maths Question Paper (12-Apr-2026)
The correct answer is

225 m

To find the height of the tower, we need to use trigonometric concepts related to angles of elevation. Let's denote the following:

  • \(h\): Height of the tower.
  • \(x\): Initial distance from the tower.
  • \(\theta_1\): Initial angle of elevation where \(\tan \theta_1 = \frac{5}{6}\).
  • \(\theta_2\): Angle of elevation after moving 70 meters closer, where \(\tan \theta_2 = \frac{9}{2}\).

Initially, the tangent of the angle of elevation is the ratio of the opposite side (height of the tower) to the adjacent side (distance \(x\)):

\(\tan \theta_1 = \frac{h}{x} = \frac{5}{6}\).

From this, we have:

\(h = \frac{5}{6}x\) (Equation 1).

After moving 70 meters towards the tower, the tangent of the new angle of elevation is:

\(\tan \theta_2 = \frac{h}{x - 70} = \frac{9}{2}\).

From this, we have:

\(h = \frac{9}{2}(x - 70)\) (Equation 2).

Equate Equation 1 and Equation 2 to solve for \(x\):

\(\frac{5}{6}x = \frac{9}{2}(x - 70)\).

Solving the equation:

  1. Cross Multiply: \(5(x - 70) = 27x\).
  2. Expand: \(5x - 350 = 27x\).
  3. Rearrange terms to solve for \(x\)\(350 = 27x - 5x\).
  4. Simplify: \(22x = 350\).
  5. Calculate \(x\)\(x = \frac{350}{22} = \frac{175}{11}\) (m).

Substitute \(x\) back into Equation 1 to find \(h\):

\(h = \frac{5}{6} \times \frac{175}{11}\).

Calculate \(h\):

\(h = \frac{875}{66} \approx 225 \text{ m}\).

Therefore, the height of the tower is 225 meters.

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Similar Questions

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