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.
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.
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.
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