Regular and Irregular Polygons

In the adjoining figure of an equilateral triangle ABC there are three sides i.e., AB, BC and CA are equal and there are three angles i.e., ∠ABC, ∠BCA and ∠CAB are equal.

Therefore, an equilateral triangle is a regular polygon.

In the adjoining figure of a square ABCD there are four sides i.e., AB, BC, CD and DA are equal and there are four angles i.e., ∠ABC, ∠BCD, ∠CDA and ∠DAB are equal.

Therefore, a square is a regular polygon.

In the adjoining figure of a regular pentagon ABCDE there are five sides i.e., AB, BC, CD, DE and EA are equal and there are five angles i.e., ∠ABC, ∠BCD, ∠CDE, ∠DEA and ∠EAB are equal.

Therefore, a regular pentagon is a regular polygon.

In the adjoining figure of a scalene triangle ABC there are three sides i.e., AB, BC and CA are unequal and there are three angles i.e., ∠ABC, ∠BCA and ∠CAB are unequal.

Therefore, a scalene triangle is an irregular polygon.

In the adjoining figure of a rectangle ABCD there are four sides i.e., AB, BC, CD and DA where the opposite sides are equal i.e., AB = CD and BC = AD. So, all the sides are not equal to each other.

Similarly, among the four angles i.e., ∠ABC, ∠BCD, ∠CDA and ∠DAB where the opposite angles are equal i.e., ∠ABC = ∠CDA and ∠BCD = ∠DAB. So, all the angles are not equal to each other.

Therefore, a square is an irregular polygon.

In the adjoining figure of an irregular hexagon ABCDEF there are six sides i.e., AB, BC, CD, DE, EF and FA are equal and there are six angles i.e., ∠ABC, ∠BCD, ∠CDE, ∠DEF, ∠EFA and ∠FAB are equal.

Therefore, an irregular hexagon is an irregular polygon.