Lines and Types of Angles

An angle measures the amount of turn between two lines meeting at a point, in degrees ($°$). Angles are classified by size:

Worked example. Classify $45°$, $90°$, $130°$, $200°$: acute, right, obtuse, reflex.

Exam checkpoint

Classify an angle by its size: acute is less than $90^\circ$, right is exactly $90^\circ$, obtuse is between $90^\circ$ and $180^\circ$, straight is $180^\circ$ and reflex is more than $180^\circ$. Use a protractor from its centre mark and read the scale that starts at zero on the correct side.

Short worked example. An angle of $125^\circ$ is obtuse because it is greater than $90^\circ$ but less than $180^\circ$.