## Summary

**Closed figure **

A figure with no open ends is a closed figure.

**Regular closed figures**

A closed figure in which all the sides and angles are equal.

**Simple curve **

A curve does not cross it self is called simple curve.

**Simple closed curve**

A curve with no open ends and does not cross it self is called simple closed curve.

**Interior region**

The portion of the plane inside the curve is called interior region.

**Exterior region**

The portion of the plane outside the curve is called exterior region.

**Perimeter**

Perimeter is the distance covered along the boundary forming a closed figure when we go round the figure once. The perimeter of a regular closed figure is equal to the sum of its sides. The concept of perimeter is widely used in real life.

e.g.

1) For fencing land.

2) For building a compound wall around a house.

**Perimeter of a rectangle**

= Length (l) + Breadth (b) + Length (l) + Breadth (b)

= 2 ( l + b)

**Perimeter of a square**

= S + S + S + S

= 4 × S.

**Equilateral triangle**

A triangle with all its sides and angles equal is called an equilateral triangle.

The perimeter of an equilateral triangle with the side 'a' = a + a + a = 3 × a