Definition: An angle whose measure is exactly 90°

Try this
Adjust the angle below by dragging an orange dot and see how the angle ∠ABC behaves.
Note that it is a right angle only when its measure is exactly 90°

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.

We say that the line segemnts AB and BC are 'at right angles' to each other. Sometimes we say that these lines are 'orthogonal' or 'normal' to each other, which is the same thing.

Acute angle Less than 90° |
Right angle Exactly 90° |
Obtuse angle Between 90° and 180° |

Straight angle Exactly 180° |
Reflex angle Between 180° and 360° |
Full angle Exactly 360° |

- Vertical angles
- Complementary angles
- Supplementary angles
- Linear pair
- Adjacent angles
- Corresponding angles
- Alternate interior angles
- Alternate exterior angles
- Interior angles of a transversal
- Exterior angles of a transversal

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