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Complementary and supplementary anglesBefore we define what we mean by complementary and supplementary angles, here is an important reminder about adjacent angles Adjacent angles: Angles that share a vertex and a common side Complementary angles: Two angles whose measures add to 90 degrees. It is easy to see when the angles are adjacent like the following: ![]() Now why are they complementary? Notice also that the angle in blue measures 90 degrees Since the measure of angle x plus the measure of angle y = 90 degrees, x and y are complementary Angles do not have to be adjacent to be complementary. The following angles are also complementary as long as the sum of the measures equal 90 degrees ![]() Two angles whose measures add to 180 degrees. It is easy too to see this when the angles are adjacent like the following: ![]() Now why are they supplementary? Notice also that the angle in blue measures 180 degrees because the angle is a striaght line and a straight line measures 180 degrees Since the measure of angle a plus the measure of angle b = 180 degrees, a and b are supplementary Again, angles do not have to be adjacent to be supplementary. The following angles are also supplementary as long as the sum of the measures equal 180 degrees ![]() |
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|Types of angles|
Complementary and supplementary angles|
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