untitled

Solution : Let, the height of the stick from the
foot learned against the tree of AB 7 metre and
angle of depression is ‘DBC 30 $
?‘ACB ‘DBC 30 $ [alternate angle]
From 'ABC we get,

BC

AB

sin‘ACB or,

BC

si

7

n 300

or, »
¼

º

«¬

ª

2

1

n 30

7

2

(^10)
si
BC

?BC 14
? Required height of the stick is 14 metre.
Activity :
In the figure, if depression angle ‘CAE 60 $,
elevation angle ‘ADB 30 $, AC 36 metre
and B,C,D lie on the same straight line, find
the lengths of the sides AB,ADandCD.
Example 5. The angle of elevation at a point of the roof of a building is 60 $ in any
point on the ground. Moving back 42 metres from the angle of elevation of the point
of the place of the building becomes 45 $. Find the height of the building.
Solution : Let, the height of the building is AB h
metres. The angle of elevation at the top ‘ACB 60 $.
The angle of elevation becomes ‘ADB 45 $ moving
back from C by CD 42 metres.
Let, BC x metre
?BD BCCD x 42 metre
From 'ABC we get,
BC
AB

tan 600 or, 3 >@tan 600 3

x

h



? (^) i
h
x ............
3
Again, from 'ABD we get,
BD
AB
tan 450

or, >@n 45 1

42

1 0



ta

x

h

 or, h x 42

or, 42 ;
3



h

h by equation (i)