Question

7. From a point on the ground, the angles of elevation of the bottom and the top of a transmission tower fixed at the top of a 20 m high building are 45° and 60° respectively as shown in Figure 3. Find the height of the transmission tower. ​

Answer 1

Let DC be the tower and BC be the building. Then,

∠CAB=45

o

,∠DAB=60

o

,BC=20 m

Let height of the tower, DC=h m.

In right △ABC,

tan45 o = AB/BC

1=20/AB

AB=20m

In right∆ABD,

tan 60°=BD/AB

√3=h+20/20

h=20(√3-1)m