LESSON: Classifying Angles



  • Classify angles as acute, right, obtuse or straight.
  • Classify angle pairs as supplementary or complementary
  • Use real-world angle pair diagrams to find unknown angle measures.


Acute angle
an angle less than 90 degrees.
Right angle
an angle equal to 90 degrees.
Obtuse angle
an angle greater than 90 degrees but less than 180 degrees.
Straight angle
a straight line equal to 180 degrees
Supplementary angles
two angles whose sum is 180 degrees.
Complementary angles
two angles whose sum is 90 degrees