5 January 2014


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 equal.


Perimeter is the distance covered along the boundary forming a closed figure when we go round the figure once. The concept of perimeter is widely used in real life.
Eg: 1) For fencing land. 
2) For building a compound wall around a house.
The perimeter of a regular closed figure is equal to the sum of its sides.

Perimeter of a rectangle:

Perimeter of a square:

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' 


The amount of surface enclosed by a closed figure is called its area.  
The following conventions are to be adopted while calculating the area of a closed figure using a squared or graph paper.
  1. Count the fully-filled squares covered by the closed figure as one square unit or unit square each.
  2. Count the half-filled squares as half a square unit.
  3. Count the squares that are more than half-filledas one square unit.
  4. Ignore the squares filled less than half.
For example, the area of this shape can be calculated as shown:
Covered area
Area estimate (sq. units)
Fully filled squares
Half–filled squares
7 x ½
Squares filled more than half
Squares filled less than half
Area covered by full squares = 6 x 1 = 6 sq. units
Area covered by half squares = 7 x ½ = 7/2= 3 ½ sq. units
Total area of the given shape = 6 + 3 ½ sq. units
Thus, the total area of the given shape = 9 ½ sq. Units
Area of a rectangle can be obtained by multiplying length by breadth.  Area of the  square can be obtained by multiplying side by side.

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