Details

If a regular polygon has an odd number of sides, then it can be dissected into isosceles triangles with the same legs. These triangles have certain kinds of angles. Specifically, a regular polygon with sides contains isosceles triangles whose third angle equals , for [1, p. 11]. For the pentagon, Frederickson calls these triangles iso-penta triangles [1, p. 212] and for the heptagon, they are called iso-hepta triangles [1, p. 218]. So in the case of the regular -gon, we call them iso- triangles.

Reference

[1] G. N. Frederickson, Dissections: Plane & Fancy, New York: Cambridge University Press, 1997.