Supplementary Angles Small 320×168 Medium 640×335 Large 1024×537 Download Tiff Original 2400×1258 | (136.6 KB) Description Illustration of supplementary angles. Two angles whose sum is a straight angle. This can be used tow show the Theorem: If two adjacent angles have their exterior sides in a straight line, these angles are supplementary. Keywords 180 degrees, angle, angles, geometry, straight line, sum, supplement, supplementary, supplements Galleries Supplementary Angles Source: G.A. Wentworth Plane And Solid Geometry (Boston: Ginn & Company, 1899) 16