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Sketching Angles and Reference Angles
Jul 2, 2024
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Lecture on Sketching Angles and Reference Angles
Introduction
Discussion on sketching angles and their reference angles.
Angle measurement and rotation.
Angle Measurement
Counterclockwise Rotation:
Angle has a
positive
measure.
Clockwise Rotation:
Angle has a
negative
measure.
Example: Positive Angle
Graphed at around +40 degrees.
Full rotation = 360 degrees.
Example: Negative Angle
Graphed at around -200 degrees.
Components of an Angle:
Initial Side:
Starting side of the angle.
Terminal Side:
Ending side of the angle.
Vertex:
Point where two sides meet.
Standard Position
Defined as positioning the initial side along the positive x-axis in an x, y coordinate system.
Example: Sketching 60 Degrees in Standard Position
Rotate in the counterclockwise direction.
Initial side along the x-axis, vertex at the origin.
Terminal side at about +60 degrees.
Example: Sketching -150 Degrees in Standard Position
Rotate in the clockwise direction.
Initial side along the x-axis, vertex at the origin.
Terminal side at about -150 degrees.
Reference Angles
Definition:
An acute angle formed by the terminal side and the x-axis.
Acute angle: Between 0 and 90 degrees (or 0 and Ο/2 radians).
Example: Sketching 120 Degrees and Identifying Reference Angle
Positive direction rotation.
Terminal side about +120 degrees.
Reference angle with the x-axis: 60 degrees (180 - 120 = 60).
Importance:
Essential in trigonometry for graphing angles accurately.
Sketching in Radians
Example: 5Ο/6 Radians
Convert radians to degrees: Ο/6 β 30 degrees.
5Ο/6 β 150 degrees (180 - 30).
Reference angle: Ο/6 radians.
Conversion Memorization: Key Angles
Ο = 180 degrees, 2Ο = 360 degrees.
Ο/6 = 30 degrees, Ο/4 = 45 degrees, Ο/3 = 60 degrees.
Essential to memorize these conversions.
More on Reference Angles
Example: -5Ο/3 Radians
Negative rotation (clockwise).
Close to -2Ο (negative full rotation).
Sketch: -5Ο/3 = -300 degrees (360 - 60).
Reference angle: Ο/3 radians (60 degrees).
Key Points of Reference Angles:
Always a positive acute angle.
The positive angle between terminal side and x-axis.
Conclusion
Importance of understanding standard position and reference angles.
Crucial for upcoming topics in trigonometry.
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