Similarity (geometry) objects similar if one appears congruent to the other when zoomed in or out at some level. For example, all circles are similar to each other, all squares are similar to each other, and all equilateral triangles are similar to each other. On the other hand, ellipses are not all similar to each other, rectangles are not all similar to each other, and isosceles triangles are not all similar to each other. If two angles of a triangle have measures equal to the measures of two angles of another triangle, then the triangles are similar. Corresponding sides of similar polygons
Regular polygon "n"-gon, the sum of the perpendicular distances from any interior point to the "n" sides is "n" times the apothem (the apothem being the distance from the center to any side). This is a generalization of Viviani's theorem for the "n"=3 case. The circumradius "R" from the center of a regular polygon to one of the vertices is related to the side length "s" or to the apothem "a" by For constructible polygons, algebraic expressions for these relationships exist; see Bicentric polygon#Regular polygons. The sum of the perpendiculars from a regular "n"-gon's vertices to any line tangent to the circumcircle