An angle is a portion of the plane defined by two half-lines of the same origin. An angle is composed of a vertex and 2 lines. It's measured in degrees or radians (180° = n rad).

• A right angle is formed when the lines are perpendicular to each other.
• An obtuse angle is larger than a right angle.
• An acute angle is smaller than a right angle.
• When both lines overlap, the angle is null.
• When both lines are opposite, the angle is flat. The straight angle contains two right angles.

Drag the red points.

Click on the set square or the protractor to measure the angles.