Introduction
The height of a building or the width of a river can be measured without climbing or crossing it. In this chapter we will show how it is made possible. Some suitable angles and distances will be measured to achieve the above results.
Heights and Distances
Angle of elevation is the angle between a horizontal line and the line joining the observer's eye to some object above the horizontal line.
Angle of depression is the angle between a horizontal line and the line joining the observer's eye to some object beneath the horizontal line.
Solved Examples
1. At a point 50 m from the foot of a building, the angle of elevation of the top of the building is 70o 36'. Find the height of the building.
2. The shadow of a vertical lower on level ground increased by 10 m when the altitude of the sun changed from 45o to 30o. Using the given figure, find the height of the tower, correct to one place of decimal.
Summary
The angle elevation and the angle of depressions are the angles which the line of sight makes with the horizontal.
The angle of elevation of A as observed from C equals the angle of depression of C as observed from A.
