Answer:
(d) 4
Explanation:
Given a diagram showing various angles between horizontal and lines of sight from an observer, you want to identify the angle of depression.
Angle of depression
An angle of depression is the angle between horizontal and the line of sight below horizontal. In the given figure, ...
angle 4 is the angle of depression
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Additional comment
When the line of sight is above horizontal, the angle is called the angle of elevation. Since horizontal lines are parallel, the angles at either end of the line of sight (angle of depression, angle of elevation) will be congruent. That means angle 3 is congruent to the angle of depression from the observer to the point at the bottom of the left structure.