Triangle pentagon erecting consists of erecting regular pentagons on the sides of a triangle; doing so internally leads to the inner pentagon point, while doing so externally gives the outer pentagon point.
Triangle Pentagon Erecting
See also
Inner Pentagon Point, Outer Pentagon PointExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Triangle Pentagon Erecting." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/TrianglePentagonErecting.html