Question

from an aeroplane vertically above a straight horizontal road, the angle of depression of 2 consecutive mile stones on opposite sides of the aeroplane are observed to be alpha and beta. show that the height in miles of aeroplane above the road is given by tan alpha tan beta divided by tan alpha + tan beta.

Answer 1

take 2 triangles CED and ABE such that CB=AB=x(height of aeroplane)
ED is on EB where EB>ED(seriously, u cn take EB<ED too)
Angle c = ALPHA
angle A= beta

now comes the fun part....

ED/x=tan alpha
x=ED/tan alpha

EB/x=tan beta
x=EB/tan beta

therefore;;
ED/tan alpha=EB/tan Beta