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A man of height 1.8 m standing 5m away from a lamp post,observes his shadow of length 1.5m.Find the height of the lamp post

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Let the hight of lamp post be x
height of man =1.8m
distance of man from lamp post =5m
distance of shadow from foot of man =1.5m
construct a triangle from given data and it will carry another triangle.they will be similar 
by similar triangle property
the ratio of corresponding sides ratio always equal
cross multiply
1.5x=1.8 X 6.5
x=7.8 m
height of lamp post is 7.8 m

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Let the height of lamp post = x m
Height of man =1.8 m
Distance of man from lamp post = 5m
Distance of shadow from foot of man =1.5m
Distance of shadow from foot of lamp post= 5 +1.5=6.5 m
Let the elevation angle the lamp makes in respect to the man Is Ф
So we have tanФ= 1.8/1.5 = x/6.5
                                 ⇒ x = 6.5*1.8/1.5
                                     x = 7.8
Hence height of lamp post is 7.8 m

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