<P> which is the optic equation . </P> <P> There are numerous triangle inequalities that hold with equality if and only if the triangle is equilateral . </P> <P> An equilateral triangle is the most symmetrical triangle, having 3 lines of reflection and rotational symmetry of order 3 about its center . Its symmetry group is the dihedral group of order 6 D . </P> <P> Equilateral triangles are the only triangles whose Steiner inellipse is a circle (specifically, it is the incircle). </P>

How many lines of symmetry has an equilateral triangle