Unit Circle & Radians
Radians measure an angle by arc length. 180° = π radians.
The rules
- To convert degrees to radians, multiply by π/180.
- Key angles: 30° (π/6), 45° (π/4), 60° (π/3), 90° (π/2).
- On the unit circle, cos is the x-coordinate and sin is the y-coordinate.
- Signs depend on the quadrant.
Watch out: Forgetting the sign in the second, third and fourth quadrants.
Worked example
Convert 150° to radians.
- 150 · π/180.
- Simplify: 5π/6.
Answer: 5π/6
Try it yourself
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