Straight Angle

Author

Eric W. Weisstein
August 14, 2026

This notebook downloaded from https://mathworld.wolfram.com/notebooks/Trigonometry/StraightAngle.nb.

For more information, see Eric's MathWorld entry https://mathworld.wolfram.com/StraightAngle.html.

©2026 Wolfram Research, Inc. except for portions noted otherwise

Illustration

The opposite rays OA and OC form the straight angle AOC, whose measure is pi radians.

Module[{angleColor,neutral,origin},
origin={0,0};angleColor=RGBColor[0.15,0.45,0.8];neutral=LightDarkSwitched[Black,White];Graphics[{Directive[angleColor,Opacity[0.2]],Disk[origin,0.6,{0,π}],Directive[angleColor,AbsoluteThickness[2.5]],Circle[origin,0.6,{0,π}],Directive[neutral,Opacity[1],AbsoluteThickness[2]],Line[{{-1.9,0},{1.9,0}}],PointSize[0.018],Point[origin],Text[Style["π",18,angleColor,FontFamily->"Times"],{0,0.83}],Text[Style["A",16,neutral,FontFamily->"Times",FontSlant->"Italic"],{2.08,0}],Text[Style["C",16,neutral,FontFamily->"Times",FontSlant->"Italic"],{-2.08,0}],Text[Style["O",16,neutral,FontFamily->"Times",FontSlant->"Italic"],{0,-0.18}]}]]