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From the foot of a tower, the angle of elevation of the top of a column is 60° and from the top of the tower, which is 25 m high, the angle of elevation is 30°. The height of the column is:

  1. 14.4 m

  2. 37.5 m

  3. 42.5 m

  4. 43.3 m

Heights & Distances

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Answer

From the foot of a tower, the angle of elevation of the top of a column is 60° and from the top of the tower, which is 25 m high, the angle of elevation is 30°. The height of the column is: Volume And Surface Area of solid RSA Mathematics Solutions ICSE Class 10.

Let AB be the tower and CD be the column.

Let distance between tower (AB) and column (BD) = x

In triangle CBD,

tan60=CDBD3=CDxx=CD3 …..(1)\Rightarrow \tan 60^{\circ} = \dfrac{CD}{BD} \\[1em] \Rightarrow \sqrt3 = \dfrac{CD}{x} \\[1em] \Rightarrow x = \dfrac{CD}{\sqrt3} \text{ …..(1)}

In triangle CAE,

tan30=CEAE13=CD25xx=(CD25)3 …..(2)\Rightarrow \tan 30^{\circ} = \dfrac{CE}{AE} \\[1em] \Rightarrow \dfrac{1}{\sqrt3} = \dfrac{CD - 25}{x} \\[1em] \Rightarrow x = (CD - 25)\sqrt3 \text{ …..(2)}

From (1) and (2), we get :

CD3=(CD25)3\dfrac{CD}{\sqrt{3}} = (CD - 25)\sqrt{3}

CD = (CD - 25)3

CD = 3CD - 75

2CD = 75

CD = 752\dfrac{75}{2}

CD = 37.5 m

Hence, option 2 is the correct option.

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