D.
an arithmetic progression
a geometric progression
a harmonic progression
an arithmetico-geometric progression
The angle of elevation of a stationary cloud from a point 2500m above a lake is 15° and from the same point the angle of depression of its reflection in the lake is 45°. The height(in metres) of the cloud above the lake, given that cot(15°) = 2 + , is
2500
5000