Supplementary Angles Small 320×130 Medium 640×259 Large 1024×415 Download TIFF Original 2400×973 | (124.9 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 are supplementary, their exterior sides are in the same straight line. 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) 17