PO is a vertical tower. P is the foot and Q is the top of the tower. A,B,C are three points in the horizontal plane through P. The angles of elevation of B from A, B ,C are equal and each is equal to θ. The sides of the triangle ABC are a, b, c and the area of the triangle AB C is Δ. Show that the height of the tower is abc tanθ/4Δ.