

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.
Talking about right angles
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.
Other angle topics
General
Angle Types
Angle relationships
(C) 2009 Copyright Math Open Reference. All rights reserved

