From an aeroplane vertically above a horizontal road, the angles of depression of two friends standing on either side of the aeroplane are observed to be α & β. The distance between the two friends is 1 m. The height (in metres) of the aeroplane from the ground is
Tan α.TanβTan α+Tan β
Let H be the height at which the aeroplane is flying.
In triangle ABD
tanβ=ADBD=HBD⇒BD=Htan β (i)
In △ ADC
tan α=ADDC=HDCDC=Htan α (ii)
Now, BD + DC = BC = 1 m
Htan β+Htan α = 1
H[1tan β+1tan α]=1H[tan α+tan βtan α.tanβ]=1H=tan α.tanβtan α+tan β