## Ch-9 Some Applications of Trigonometry

**Line of Sight**

When an observer looks from a point E (eye) at an object O then the straight line EO between the eye E and the object O is called the line of sight.

**Horizontal**

When an observer looks from a point E (eye) to another point Q which is horizontal to E, then the straight line, EQ between E and Q is called the horizontal line.

**Angle of Elevation**

When the eye is below the object, then the observer has to look up from the point E to the object O. The measure of this rotation (angle θ) from the horizontal line is called the angle of elevation.

**Angle of Depression**

When the eye is above the object, then the observer has to look down from the point E to the object. The horizontal line is now parallel to the ground. The measure of this rotation (angle θ) from the horizontal line is called the angle of depression.

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