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Meaning of exterior angle

exte'rior an'gle

Pronunciation: [key]
— Geom. Geom.
  1. an angle formed outside parallel lines by a third line that intersects them. See diag. under
  2. an angle formed outside a polygon by one side and an extension of an adjacent side; the supplement of an interior angle of the polygon.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.