What kinds of polygons are symmetrical?

Answer 1

All regular polygons

A polygon is symmetrical if its sides that cross the line of symmetry are halved by the line of symmetry and if the sides that do not cross the line of symmetry have the same positions in space, the same lengths, and the same angles with their neighboring sides as do the sides on the other side of the line of symmetry. The only symmetrical triangles are isosceles triangles (equilateral triangles are isosceles). The only symmetrical quadrilaterals are squares, rectangles, rhombi (the line of symmetry connects either pair of opposite corners), isosceles trapezoids, and kites.