# Right angle

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.

In the figure above, press 'reset' to ensure ABC 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.

## Types of angle

Altogether, there are six types of angle as listed below. Click on an image for a full description of that type and a corresponding interactive applet.   Acute angleLess than 90° Right angleExactly 90° Obtuse angleBetween 90° and 180°   Straight angleExactly 180° Reflex angleBetween 180° and 360° Full angleExactly 360°