Notes
angle

Angle

An angle is a measure of turn. More precisely, the angle formed between two lines at their intersection point is a measure of how much one line should be rotated about that point to lie along the second line.

Angles can be signed or unsigned, if signed then the convention is that positive angles are anti-clockwise and negative angles clockwise.

There are different units when measuring angles:

• degrees a full turn is $360^\circ$
• radians a full turn is $2\pi$ radians

There are several types of angle:

• An acute angle is an angle between no turn and a quarter turn
• A right-angle is a quarter of a turn
• An obtuse angle is an angle between a quarter turn and a half turn
• A reflex angle is an angle between a half turn and a full turn