Understand
Angle of depression and angle of elevation
If an
object is below the horizontal line from the eye, we have to lower our head to
view the object. In this process our eyes moves through an angle. This angle
is called the angle
of depression, That is, the angle of depression of an object viewed is the angle
formed by the line of sight with the horizontal line, when the object is below
the horizontal line
If an
object is above the horizontal line from our eyes we have to raise our head to
view the object. In this process our eyes move through an angle formed by the
line of sight and horizontal line which is called the angle
of elevation.
Note :
1.
An observer is taken as a point if
the height of the observer is not given.
2.
The angle of elevation of an object
as seen by the observer is same as the angle of
depression
of the observer as seen from the object.
Example 1
A kite is flying
with a string of length 200 m. If the thread makes an angle 30c with the
ground, find the distance of the kite from the ground level. (Here, assume that
the string is along a straight line)
Example 2
A ladder leaning
against a vertical wall, makes an angle of 60 degree with the ground. The foot of the ladder
is 3.5 m away from the wall. Find the length of the ladder.
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