Question
A vertical tower stands on a horizontal plane and is surmounted by a vertical flagstaff of height y. At a point on the plane, the angles of elevation of the bottom and the top of the flagstaff are a and fi respectively. Prove that the height of the tower is 
Solution
Let BD be the tower of height h m and CD be the flagstaff of height y m. Let A be the point on the plane such that the angles of elevation of the bottom and top of the flagstaff are α and β respectively.
Let AB = x metres.
In right triangle ABD, we have
In right triangle ABC, we have
Comparing (i) and (ii), we get
