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Classify angles

Angles are classified by their measure in degrees as acute (less than 90°), right (exactly 90°), obtuse (greater than 90° but less than 180°), or straight (exactly 180°), regardless of their orientation or the lengths of their rays. This understanding distinguishes an angle’s opening from the size of its drawing and supports reasoning about geometric figures, angle relationships, and measurement.

Detailed Explanation: Classify angles

To classify an angle, look at its measure in degrees and compare it with 90∘90^\circ and 180∘180^\circ. The direction the angle points and the lengths of its rays do not matter.

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

Example: Classify an angle measuring 125∘125^\circ.

  1. Compare 125∘125^\circ with 90∘90^\circ:
125∘>90∘125^\circ > 90^\circ
  1. Compare 125∘125^\circ with 180∘180^\circ:
125∘<180∘125^\circ < 180^\circ
  1. Therefore, 125∘125^\circ is greater than 90∘90^\circ but less than 180∘180^\circ.

So, the angle is obtuse.

Learn by doing: Classify angles

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    Angles - Acute, Obtuse, Right or Straight

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