Geometry

UK Secondary (7-11)

Classifying an Angle

Lesson

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 angles are angles that sum to $90$90°. In the diagram on the right, $\angle DOC$∠`D``O``C` and $\angle COB$∠`C``O``B` are complementary.

Supplementary angles are angles that sum to $180$180°. In the diagram on the right, $\angle COD$∠`C``O``D` and $\angle DOE$∠`D``O``E` 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°

Is this angle acute, obtuse or reflex?