A rotation through ( radians).
Half-Turn
See also
RotationExplore with Wolfram|Alpha
References
Coxeter, H. S. M. and Greitzer, S. L. "Half-Turn." §4.3 in Geometry Revisited. Washington, DC: Math. Assoc. Amer., pp. 85-86, 1967.Referenced on Wolfram|Alpha
Half-TurnCite this as:
Weisstein, Eric W. "Half-Turn." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Half-Turn.html