# NCERT Notes for Class 10 Maths Chapter 9 Some Applications of Trigonometry

#### Class 10 Maths Chapter 9 Some Applications of Trigonometry Notes

 Chapter Name Some Applications of Trigonometry Notes Class CBSE Class 10 Textbook Name NCERT Mathematics Class 10 Related Readings Notes for Class 10Notes for Class 10 MathsRevision Notes for Some Applications of Trigonometry

#### Line of Sight

When an observer looks from a point E (eye) at object O then the straight line EO between eye E and object O is called the line of sight.

#### Horizontal

When an observer looks from a point E (eye) to another point Q which is horizontal to E, then the straight line, EQ between E and Q is called the horizontal line.

#### Angle of Elevation

When the eye is below the object, then the observer has to look up from point E to object O. The measure of this rotation (angle Î¸) from the horizontal line is called the angle of elevation.

#### Angle of Depression

When the eye is above the object, then the observer has to look down from point E to the object. The horizontal line is now parallel to the ground. The measure of this rotation (angle Î¸) from the horizontal line is called the angle of depression.

### How to convert the above figure into the right triangle

#### Case I: Angle of Elevation is known

Draw OX perpendicular to EQ.
Now ∠OXE = 90°
Î”OXE is a rt. Î”, where
OE = hypotenuse
OX = opposite side (Perpendicular)

#### Case II: Angle of Depression is known

(i) Draw OQ’parallel to EQ
(ii) Draw perpendicular EX on OQ’.
(iii) Now ∠QEO = ∠EOX = Interior alternate angles
Î”EXO is an rt. Î”. where
EO = hypotenuse
EX = opposite side (Perpendicular)

• Choose a trigonometric ratio in such a way that it considers the known side and the side that you wish to calculate.
• The eye is always considered at ground level unless the problem specifically gives the height of the observer.

The object is always considered a point.
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