251Angles 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.

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