Notes of chapter: Mensuration| Perimeter| Area| Surface area| Volume are presented below. Indepth notes along with worksheets and NCERT Solutions.
(1) Total length of outline of a closed figure is known as perimeter of that figure.
(i) Perimeter of polygons-
(a) Perimeter of any equilateral polygon is multiplication of sides with number of sides.
Perimeter of an equilateral polygon = n × side
Where, n = number of sides of equilateral polygon
Therefore perimeter of square, rhombus, equilateral triangle, equilateral pentagon or any other equilateral polygon can be calculated by above formula.
(A)Perimeter of a square = n × side
Where, n = number of sides of square
Perimeter of a square = 4 × side
Eg:- Find the perimeter of square ABCD whose one side is 3 cm.
Ans-
(B) Perimeter of a rhombus = n × side
Where, n = number of sides of rhombus
Perimeter of a rhombus = 4 × side
Eg:- Find the perimeter of rhombus ABCD whose one side is 3 cm.
Ans-
(C) Perimeter of an equilateral triangle = n × side
Where, n = number of sides of an equilateral triangle
Perimeter of an equilateral triangle = 3 × side
Eg:- Find the perimeter of equilateral triangle ABC whose one side is 3 cm.
Ans-
(D) Perimeter of an equilateral pentagon = n × side
Where, n = number of sides of an equilateral pentagon
Perimeter of an equilateral pentagon = 5 × side
Eg:- Find the perimeter of equilateral pentagon ABCDE whose one side is 3 cm.
Ans-
(b) Perimeter of general polygons –
Perimeter of general polygons can be calculated by adding lengths of the all sides of the general polygon.
Perimeter of general polygon = sum of the all sides of general polygon
Therefore, perimeter of parallelogram, rectangle, trapezium or any other shape can be calculated by adding all sides of that shape.
(A)Perimeter of parallelogram = sum of all sides
Eg:- Find the perimeter of parallelogram ABCD whose one side(AB) is 3 cm and other side (BC) is 2 cm.
Ans-
(B) Perimeter of a rectangle = 2 × (l + b)
Where,
l = length of the rectangle
b = breadth of the rectangle
Eg:- Find the perimeter of rectangle ABCD whose one side(AB) is 3 cm and other side (BC) is 2 cm.
Ans-
(C)Perimeter of triangle = sum of all sides
Eg:- Find the perimeter of triangle ABC whose sides are 7 cm, 4 cm and 10 cm.
Ans-
(iv) Surface area of a right circular cone
A right circular cone is a hollow cone in which surface area is generated by a perpendicular line which is passes through center of the circular base.
The cone is made up of small triangles as shown in figure below-
Helping Topics