9. Some Applications of Trigonometry

Class X

Exercise 9.1

NCERT Textbook Solution

Learning Points

• Angle of Elevation
• Angle of Depression

Angle of Elevation

The angle between line of sight and horizontal level when the observer is below the object is said to be angle of elevation.

Angle of Depression

The angle between line of sight and horizontal level when the observer is above the object is said to be the angle of depression.

Exercise 9.1

Q.No.1. 

 A circus artist is climbing a 20 m long rope, which is tightly stretched and tied from the top of a vertical pole to the ground. Find the height of the pole, if the angle made by the rope with the ground level is 30° (see Fig. 9.11).

Fig. 9.11

Solution:

From question it is clear that

Angle of Elevation = Ө = 30°

Height of the pole = AB = ?

Now applying trigonometric ratio sin𝞱

From figure it is clear that

sin𝞱 = AB/AC

Now putting the value of 

1/2 = AB/20

AB = 10 m Ans.