Page 102 - Maths Skill - 6

100 Maths

PERIMETER OF TRIANGLE
(i) Scalene Triangle A

A scalene triangle is a triangle in which all three sides are of different lengths.
Consider a triangle having three given sides of lengths 5 cm, 7 cm and 8 cm.
Find its perimeter. 5 cm 7 cm
Perimeter of the triangle ABC = AB + BC + CA
Perimeter of the triangle = 5 cm + 8 cm + 7 cm = 20 cm.

(ii) Isosceles Triangle B 8 cm C
An isosceles triangle is a triangle that has two sides of equal length
Consider an isosceles triangle having three given sides of lengths 6 cm, 6 cm and 5 cm. Find its perimeter.

Perimeter of the triangle PQR = PQ + PR + QR
Perimeter of the triangle = 6 cm + 6 cm + 5 cm = 17 cm.

Note: Perimeter of a triangle = sum of the lengths of its three sides.

PERIMETER OF REGULAR SHAPES
A D
Perimeter of A Square
A square is a polygon (or a quadrilateral) with four equal sides.
Let’s consider a square ABCD as shown in Fig.

Perimeter of square ABCD = AB + BC + CD + DA B 5 cm C
= AB + AB + AB + AB = 4 × AB [ AB = BC = CD = DA]

Perimeter of a square = 4 × side

Perimeter of an Equilateral Triangle
An equilateral triangle is a triangle with all the sides equal. A

Let’s take an equilateral ∆ABC, as shown in Fig.
Here, AB = BC = CA
So, Perimeter of DABC = AB + BC + CA

= AB + AB + AB B C
= 3 × AB

or Perimeter of an equilateral ∆ = 3 × side
Similarly, perimeter of other regular polygons would be:

Perimeter of a regular Pentagon = 5 × side
Perimeter of a regular Hexagon = 6 × side
Perimeter of a regular Heptagon = 7 × side
Perimeter of a regular Octagon = 8 × side

and Perimeter of a regular polygon with ‘n’ side = n × side