Angles of Elevation and Depression
Let us assume that is a tower. being the top point and being the base of the tower.
Also assume that is height where the eye is.
Therefore is the line of sight.
Therefore, if one is going to see the top of the tower from point , then the is the angle of elevation.
Similarly, if the person was at point and was trying to see , then is the angle of depression.
Since (alternate angles).
Hence, angle of elevation is always equal to the angle of depression.