Skill: Identify acute, right, obtuse, and straight angles

To classify an angle, look at its measure in degrees. Compare it with $90^\circ$ and $180^\circ$:

• Acute: less than $90^\circ$
• Right: exactly $90^\circ$
• Obtuse: greater than $90^\circ$ but less than $180^\circ$
• Straight: exactly $180^\circ$

Example

Classify an angle that measures $125^\circ$.

1. Compare $125^\circ$ with $90^\circ$:

$$125^\circ > 90^\circ$$

2. Compare $125^\circ$ with $180^\circ$:

$$125^\circ < 180^\circ$$

3. Therefore, $125^\circ$ is greater than $90^\circ$ but less than $180^\circ$.

Answer: The angle is obtuse.

The direction the angle points and the lengths of its rays do not change its classification. Only the size of its opening matters.