If Mary measures the angle of elevation from a point A, to be 10°. She then walks 100m directly towards the tower, and finds the angle of elevation from the new point B to be 20°, the height of the tower comes out to be 37 meters.
Given Information and Formula Used:
The angle of elevation of the tower from point A (a in figure) = 10°
The angle of elevation of the tower from point B (b in figure) = 20°
The distance AB (ab n figure) = 100m
In right triangle adc, tan 10° = cd / ad ....... (1)
In right triangle bdc, tan 20° = cd / bd ......... (2)
Here, cd is the height of the tower.
Let the distance bd be x, then the ad = x + 100
Substituting this value of of ad in equation (1), we get,
tan 10° = cd / (x+100)
x+100 = cd / tan 10°
x+100 = cd / 0.18
x+100 = 5.6 cd ....... (3)
From equation (2),
tan 20° = cd / x
x = cd / tan 20°
x = cd / 0.34
x = 2.9 cd
Putting this value of x in equation (3), we obtain the height cd (or CD) as,
2.9 cd + 100 = 5.6 cd
(5.6 - 2.9)cd = 100
2.7cd = 100
cd = 100/2.7
cd ≈ 37m (To the nearest tenth of a meter)
Therefore, the height of the tower is calculated to be 37 meters.
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