# On the level ground, the angle of elevation of a tower is 30°. On moving 20 m nearer, the angle of elevation is 60°. The height of the tower isA. 10 mB. 10√3 mC. 15 mD. 20 m

Let AB be the tower and C, D are two points on the ground. Join B, C, D. Also, join A with C and D. We get two right-angled triangles ABC and ABD with right angle at B. The angles of elevation of the top of the tower from the points D and C are 30° and 60° respectively. So, ADB = 30° and ACB = 30°. We are to find the height of the tower. Also given that the distance from D to C is 20 m. So CD = 20 m.

In ∆ABC,

or,

In ∆ABD,

or,

or,

or,

So, the correct option is (B).

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