Co-terminal and Reference Angles

Co-terminal angles are angles that share the same terminal side when drawn in standard position. They can be found by adding or subtracting multiples of 360° (or 2π radians).

To convert degrees to radians, multiply the degree measure by $$\frac{\text{π}}{180}$$ .

The reference angle is the acute angle formed by the terminal side of an angle and the x-axis. It is always positive and less than 90°.

For an angle in the second quadrant, the reference angle is found by subtracting the angle from 180°. For example, for 120°, the reference angle is 180° - 120° = 60°.

$$\frac{3\text{π}}{2}$$ .

$$60°$$ .

$$285°$$ and $$-435°$$ .

To convert radians to degrees, multiply the radian measure by $$\frac{180}{\text{π}}$$ .

$$120°$$ .

$$35°$$ (since $$395° - 360° = 35°$$ ).