Right angles are one of the most common and interesting angles in all of geometry. It even has its own angle symbol. In the figure above, set the angle to 90° and see that instead of a small arc, the angle is marked with a small square symbol. If you see this, the angle measure in degrees is usually omitted. Note also that right triangles are those where one interior angle is a right angle.
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Acute angle Less than 90° |
Right angle Exactly 90° |
Obtuse angle Between 90° and 180° |
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Straight angle Exactly 180° |
Reflex angle Between 180° and 360° |
Full angle Exactly 360° |