Mensuration

Perimeter is the distance covered along the boundary forming a closed figure when you go round the figure once.

- (a) Perimeter of a rectangle = 2 × (length + breadth)
(b) Perimeter of a square = 4 × length of its side
(c) Perimeter of an equilateral triangle = 3 × length of a side
(d) Perimeter of a regular pentagon has five equal sides = 5 × length of a sides

- Figures in which all sides and angles are equal are called regular closed figures.

- The amount of surface enclosed by a closed figure is called its area.

- To calculate the area of a figure using a squared paper, the following conventions are adopted :
(a) Ignore portions of the area that are less than half a square.
(b) If more than half a square is in a region. Count it as one square.
(c) If exactly half the square is counted, take its area as 1 / 2 sq units.
 

- Area: The amount of surface enclosed by a closed figure.

- (a) Area of a rectangle = length × breadth
(b) Area of a square = side × side