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Angles HTML5

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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.

Learning goals

  • Recognize geometric properties of an angle.
  • Classify angles by name according to their measurements.
  • Use the protractor and the set square to perform angle measurements.


Learn more

An angle is measured with a protractor which represents a half circle divided into 180 sections. Each section measures 1°. It's the unit of measure for angles. To measure an angle, you…

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