**Important Concepts and Formulas**

1. The perimeter is the distance around
a closed figure.

3. Perimeter of a square = 4 × length of
a side.

4. Perimeter of a triangle = sum of all
its sides.

5. The total distance around a circle is
called its circumference.

7. The ratio of the circumference of a
circle to its diameter is denoted using the notation ‘Ï€’.

9. Perimeter of a regular polygon =
(Number of sides of polygon) × (length of a side).

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

11. Area of a rectangle = length ×
breadth.

12. Area of a square = side × side.

14. Area of a triangle = 1/2 × base ×
height.

16. The perimeter is expressed in the
same unit as the length and the breadth.

17. The units of area are square units,
such as 1 cm

^{2}= 100 mm^{2}; 1 m^{2}= 10,000 cm^{2}; 1 km^{2}= 10,00,000 m^{2}; 1 hectare = 10,000 m^{2 }; 1 acre = 4046.86 sq. m.