1 of 10

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MOUNT EVEREST

What is its height ?

How can we measure it ?

It is impossible to measure it with the help of a measuring tape.

2 of 10

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What is its width ?

It is difficult and impractical to measure it with the help of a measuring tape.

RIVER

3 of 10

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What is its height ?

How can we measure it ?

Hey…Its looking beautiful.

Yes

EIFFEL TOWER

It is impossible to measure it with the help of a measuring tape.

4 of 10

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Such Heights and Distances can be found

by Applying TRIGONOMETRY.

5 of 10

We need to learn few important terms :

  1. Line of sight
  2. Horizontal line
  3. Angle of Elevation
  4. Angle of Depression

Hi…… !

I am Raj

I am going to explain you all the important terms.

6 of 10

LINE OF SIGHT

I am observing the cow

Observer

Object

This imaginary line is connecting the eye of the observer and the object.

This line is called �‘Line of sight’

Line of sight

Let us see few more examples

Now, I am observing the door of the tree house

Observer

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Line of sight

Now, I am observing the beautiful flower

Observer

Object

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Line of sight

Object

Observer

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Line of sight

I want that apple

Object

7 of 10

ANGLE OF ELEVATION

θ

This line passes through the eye of the observer

and is parallel to the ground.

Horizontal line

This line is called ‘Horizontal line’.

I am observing the top of the tree.

Observer

?

Line of sight

Is this line of sight making an angle with the horizontal line?

YES

This angle is �called as �‘Angle of Elevation’.

: Remember : �Angle of Elevation is formed, when the object is above the horizontal line.

Object

8 of 10

ANGLE OF DEPRESSION

θ

Horizontal line

I am observing the flower on the ground.

Observer

?

Line of sight

Is this line of sight making an angle with the horizontal line?

YES

This angle is �called as �‘Angle of Depression’.

: Remember : �Angle of Depression is formed, when the object is below the horizontal line.

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Object

9 of 10

Let us revise all the four terms.

Horizontal line

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Object

I am observing the Eagle in the sky.

Observer

?

Line of sight

Object

I am observing the flower on the ground.

Observer

?

Line of sight

Angle of Elevation

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Angle of Depression

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10 of 10

  1. All the heights of objects such as towers, trees, buildings, etc.

shall be considered as a ‘line segment perpendicular to the ground’.

2. The height of the observer is neglected, if it is not given

in the problem. It shall be considered as a ‘point’.

Points to be remembered while drawing the figures to solve the problems :