Q: The points A,B & C lie in a straight line with AB=x & BC=2x. A vertical tower OH is of height h and its base O lies in the same horizontal plane as ABC but not on the line ABC.

The angle of elevation of H from A,B & C are alpha, beta & alpha respectively.

(i) prove thah h^2(cot^2(alpha) - cot^2(beta)) = 2x^2

I'm stuck and cant find another worked example of this knid anywhere. Can you help??