From a window 'h' m high above the ground of a house on a street, the angle of elevation and depression of the top and foot of another house on the opposite side of the street are α and β respectively.
The height of the opposite house is
3
Let the height of the other house be DC
DC=(h+y)m
Let the distance between the two houses = x
In Δ BFC
tan β=hx
x=htan β …(i)
In Δ BFD
tan α=yx
tan α=yhtan β ......from (i)
tan α=y tan βh
∴ y=h tan αtan β
Height of the other house = h+y
=h+htan αtan β
=h(1+tan αtan β)
=h(1+tan αcotβ)