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Angles are classified by their measures.
An acute angle measures less than 90°.
A right angle measures 90°. The small square at the vertex of this angle indicates that the
angle is a right angle.
An obtuse angle measures between 90° and 180°.
A straight angle is formed by two opposite rays.
It measures 180°.
Some Angles Travel in Pairs
If the sum of the measures of two angles is 90°, then the angles are complementary. If their sum is 180°,
then the angles are supplementary.
