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Mathematics

The distance between two multi-storeyed buildings is 60 m. The angle of depression of the first building as seen from the top of the second building, which is 150 m high, is 30°. The height of the first building is :

  1. 115.36 m

  2. 117.85 m

  3. 125.36 m

  4. 128.34 m

Heights & Distances

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Answer

The distance between two multi-storeyed buildings is 60 m. The angle of depression of the first building as seen from the top of the second building, which is 150 m high, is 30°. The height of the first building is : Volume And Surface Area of solid RSA Mathematics Solutions ICSE Class 10.

Let AB be the height of first building and CD be the height of second building.

The distance between the buildings (BD) = 60 m.

CE is the difference in height between the two buildings.

In triangle AEC,

tan30=CEAE13=CE60CE=603CE=34.64 m.\Rightarrow \tan 30^{\circ} = \dfrac{CE}{AE} \\[1em] \Rightarrow \dfrac{1}{\sqrt3} = \dfrac{CE}{60} \\[1em] \Rightarrow CE = \dfrac{60}{\sqrt3} \\[1em] \Rightarrow CE = 34.64 \text{ m}.

Height of first building,

AB = CD - CE

= 150 - 34.64

= 115.36 m.

Hence, option 1 is the correct option.

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