The angle of elevation of the top of a tower from a point A (on the ground) is 30 degree. On walking 50m towards the tower, the angle of elevation is found to be 60 degree. Calculate
(I) the height of the tower (correct to one decimal place)
(II) the distance of the tower from A.
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From ΔABC:
tan (θ) = opp/adj
tan (30) = BC/AB
BC = AB tan (30)
From ΔBCD:
tan (θ) = opp/adj
tan (60) = BC/BD
BC = BD tan (60)
Equate the 2 equations:
AB tan (60) = BD tan (30)
Define x:
Let BD = x
AB = x + 20
Solve x:
AB tan (30) = BD tan (60)
(x + 20) tan (30) = x tan (60)
x tan (30) + 20 tan (30) = x tan (60)
x tan (60) - x tan (30) = 20 tan (30)
x ( tan (60) - tan (30) ) = 20 tan (30)
x = 20 tan (30) ÷ ( tan (60) - tan (60) )
x = 10 m
Find the distance:
Distance = 10 + 20 = 30 m
Find the height:
tan (θ) = opp/adj
tan (60) = BC/10
BC = 10 tan (60) = 10√3 m
Answer: Distance = 30 m and height = 10√3 m
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Answer:From ΔABC:
tan (θ) = opp/adj
tan (30) = BC/AB
BC = AB tan (30)
From ΔBCD:
tan (θ) = opp/adj
tan (60) = BC/BD
BC = BD tan (60)
Equate the 2 equations:
AB tan (60) = BD tan (30)
Define x:
Let BD = x
AB = x + 20
Solve x:
AB tan (30) = BD tan (60)
(x + 20) tan (30) = x tan (60)
x tan (30) + 20 tan (30) = x tan (60)
x tan (60) - x tan (30) = 20 tan (30)
x ( tan (60) - tan (30) ) = 20 tan (30)
x = 20 tan (30) ÷ ( tan (60) - tan (60) )
x = 10 m
Find the distance:
Distance = 10 + 20 = 30 m
Find the height:
tan (θ) = opp/adj
tan (60) = BC/10
BC = 10 tan (60) = 10√3 m
Answer: Distance = 30 m and height = 10√3 m
Step-by-step explanation:
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