9.1 Angles and the unit circle
Unit 9 · Trigonometric functions and equations
Ideas in this lesson
Degree and radian measure
One half-turn is pi radians or 180 degrees. Convert using a factor equal to one.
Coterminal angles
Add or subtract complete turns. Use a half-open interval so its endpoints are not counted twice.
Reference angles
A reference angle is the acute angle between the terminal ray and the horizontal axis.
Sector area
A sector is a fraction of a full disk; use half the radius squared times the angle in radians.
Arc length and sectors
Use radians for arc length and sector area formulas.
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