are the angles of the top of a vertical tower from three distinct points A, B, and C, on a horizontal line that is on the same level as the base of the tower but does not necessarily pass through it. The distances AB=BC=d. Prove that the height h of the tower is given by

If , prove that the line ABC passes through the base of the tower.

I have already shown the h is given by , but i don't how to prove that if the line passes through the base of the tower.

Thanks for any help!