UK Secondary (7-11)
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Classifying an Angle


Now, let me show you different types of angles.  Play with this applet to explore the different types of angles, what they look like and how big they are. Slide the slider and watch the angle change.  


Complementary and Supplementary

Complementary angles are angles that sum to  $90$90°.  In the diagram on the right, $\angle DOC$DOC and $\angle COB$COB are complementary.

Supplementary angles are angles that sum to $180$180°. In the diagram on the right, $\angle COD$COD and $\angle DOE$DOE are supplementary angles.


Acute: an angle between 0° and 90°

Right: an angle of exactly 90° 

Obtuse: an angle of between 90° and 180°

Straight: an angle of exactly 180° 

Reflex: an angle of between 180° and 360°

Revolution: an angle of exactly 360°

Complementary: angles that sum to 90°

Supplementary: angles that sum to 180°

Worked Example

Is this angle acute, obtuse or reflex?

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