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Angle Types

A right angle is 90°.



An acute angle is an angle less than 90°.
Angle a is an acute angle.

An obtuse angle is an angle more than 90° and less than 180°.
Angle b is an obtuse angle.

A straight angle is a straight line, or 180°.
Angle c is a straight angle.



A reflex angle is more than 180° and less than 360°.

Complementary angles sum to 90°.

In a right angle triangle the two acute angles are complementary because all three angles sum to 180°.

Supplementary angles sum to 180°.

Angles that sum to 360° are called explementary angles or conjugate angles. (These names are not part of the NCEA or IGCSE syllabuses.)