Triangle triangle erecting consists of erecting equilateral triangles on the sides of a triangle; doing so internally leads to the inner Napoleon triangle, while doing so externally gives the outer Napoleon triangle.
Triangle Triangle Erecting
See also
Inner Napoleon Triangle, Outer Napoleon TriangleExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Triangle Triangle Erecting." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/TriangleTriangleErecting.html