Regular polygons are equiangular and equilateral, either convex or star. All vertices lie on a common circle and have a tangent incircle. Regular polygons have rotational symmetry of order n. The symmetry group is dihedral group Dn (order 2n)
Interior angle is formed inside a shape's two adjacent sides. Polygons can be regular (all angles equal) or irregular. Sum of interior angles equals 180°(n-2) for polygons of n sides
Diagonal is a straight line connecting opposite vertices of a shape. Diagonals are always straight lines, not going up, down or across. Diagonal comes from Greek "diagonios" meaning "from angle to angle"
Polygons are two-dimensional closed shapes formed by three or more line segments. The word 'polygon' comes from Greek 'poly' (many) and 'gon' (angle). Polygons are always closed plane shapes with only length and width dimensions
Interior angles are formed when parallel lines are cut by a transversal. Two types exist: co-interior angles on same side and alternate interior angles on opposite sides. Interior angles of a polygon always equal the number of sides
Area formula: 1/2 x perimeter x apothem. Apothem is segment joining center to perpendicular side midpoint. Perimeter found by summing all sides or multiplying side by number