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supplementary angle

American  

noun

Mathematics.
  1. either of two angles that added together produce an angle of 180°.


supplementary angle British  

noun

  1. either of two angles whose sum is 180° Compare complementary angle

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of supplementary angle

First recorded in 1830–40