Classify angles

An angle is classified by the amount of turn between its two rays, regardless of its orientation or the lengths of its sides. An acute angle measures less than 90°, a right angle measures exactly 90°, and an obtuse angle measures more than 90° but less than 180°; visual representations can be compared with a right-angle benchmark. Classification at this level does not include reflex angles or more advanced angle relationships.

Detailed Explanation: Classify angles

An angle is classified by how wide its turn is, not by which way it points or how long its sides are.

Use a right angle, which measures $90^\circ$ , as a benchmark:

Acute: less than $90^\circ$
Right: exactly $90^\circ$
Obtuse: more than $90^\circ$ but less than $180^\circ$

Example

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

Compare $125^\circ$ with $90^\circ$ .
Since $125^\circ$ is greater than $90^\circ$ , the angle is wider than a right angle.
Since $125^\circ$ is less than $180^\circ$ , it is not a straight angle.

Therefore, an angle measuring $125^\circ$ is obtuse.

Learn by doing: Classify angles

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Angles - Acute, Obtuse, Right or Straight

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