Angles of Elevation and Depression

Let us assume that $AB$ is a tower. $A$ being the top point and $B$ being the base of the tower.

Also assume that $C$ is height where the eye is.

Therefore $CA$ is the line of sight.

Therefore, if one is going to see the top of the tower $A$ from point $C$, then the $\angle ACB$ is the angle of elevation.

Similarly, if the person was at point $A$ and was trying to see $C$, then $\angle DAC$ is the angle of depression.

Since $BC \parallel DA, \angle ACB = \angle DAC$ (alternate angles).

Hence, angle of elevation is always equal to the angle of depression.