Problem 1 :
From the top of a tree of height 13 m the angle of elevation and depression of the top and bottom of another tree are 45° and 30° respectively. Find the height of the second tree. (√3 = 1.732)
Solution :
AB = 13 m = DC
In triangle AED,
tan 45 = ED/AD
1 = ED/AD
AD = ED --(1)
In triangle ABC,
tan 30 = AB/BC
1/√3 = 13/BC
BC = 13√3 ----(2)
AD = BC
By applying the value of AD in (1), we get
ED = 13√3
height of second tree = ED + DC
= 13√3 + 13
= 13(√3 + 1)
= 13(1.732 + 1)
= 13(2.732)
= 35.516 m
Hence the height of the second tree is 35.52 m
Problem 2 :
A man is standing on the deck of a ship, which is 40 m above water level. He observes the angle of elevation of the top of a hill as 60° and the angle of depression of the base of the hill as 30° . Calculate the distance of the hill from the ship and the height of the hill. (√3 = 1.732)
Solution :
In triangle AED,
tan 60 = ED/AD
√3 = ED/AD
AD = ED/√3 -----(1)
In triangle ABC,
tan 30 = AB/BC
1/√3 = 40/BC
BC = 40√3 -----(2)
BC = AD
(1) = (2)
40√3 = ED/√3
ED = 40√3(√3)
= 40(3)
ED = 120 m
Height of hill = ED + DC
= 120 + 40
= 160 m
Distance from hill to ship = 40√3
= 40(1.732)
= 69.28 m
Problem 3 :
If the angle of elevation of a cloud from a point ‘h’ meters above a lake is θ1 and the angle of depression of its reflection in the lake is θ2 . Prove that the height that the cloud is located from the ground is h(tan θ1+ tan θ2)/(tan θ2 - tan θ1)
Solution :
In triangle AED,
tan θ1 = ED/AD
tan θ1 = x/AD
AD = x/tan θ1
AD = x cot θ1 -----(1)
In triangle ADC,
tan θ2 = DC/AD
tan θ2 = (2h + x)/AD
AD = (2h + x)/tan θ2
AD = (2h + x)cot θ2 -----(2)
(1) = (2)
x cot θ1 = (2h + x)cot θ2
x cot θ1 = 2h cot θ2 + x cot θ2
x (cot θ1 - cot θ2) = 2h cot θ2
x (tan θ2 - tan θ1)/(tan θ1 tan θ2) = 2h (1/tan θ2)
2h = [xtan θ2(tan θ2 - tan θ1)]/(tan θ1 tan θ2)
2h = x(tan θ2 - tan θ1)/tan θ1
x = 2h tan θ1/(tan θ2 - tan θ1)
height of cloud = x + h
= [2h tan θ1/(tan θ2 - tan θ1)] + h
= [2h tan θ1+ h(tan θ2 - tan θ1)]/(tan θ2 - tan θ1)]
= h[tan θ1+ tan θ2]/(tan θ2 - tan θ1)]
Hence proved.
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