Perimeter

The perimeter of a two-dimensional figure is the distance covered around it. It defines the length of shape, whether it is a triangle, square, rectangle or a circle. Area and perimeter are the two major properties of a 2D shape, which describes them.

The perimeter of each shape varies as per their dimensions. Only in the case of a circle, the perimeter is stated as the circumference of the circle. But the method to find the perimeter of all the polygons is the same, which is we need to add all its sides.

If we need to calculate the length of a circular or rectangular field, then by the help of the perimeter formula we can easily find it, given the dimensions. Let us learn here formula to find perimeter for all the two-dimensional shapes.

Also, read:

Formula

Here is the list of formulas of the perimeter for all the 2d-shapes.

Name of the Shape Perimeter Formula
Circle 2πr
Triangle a+b+c, where a,b and c are the sides of triangle
Square 4a, where a is the length of side of square
Rectangle 2(L+B), where L is length and B is breadth
Quadrilateral Sum of all four sides: a+b+c+d
Parallelogram 2(a+b), where a and b are adjacent sides
Any Polygon Sum of all the sides

How to Find Perimeter

We will solve here some of the example questions to understand how to find the perimeter of different shapes.

Question.1: What is the perimeter of an equilateral triangle whose side length is 7cm?

Answer: Given, length of the side of equilateral triangle is 7cm

As we know, the equilateral triangle has all its sides equal in length.

Therefore,

Perimeter of triangle = a+b+c

Here,

a=b=c

Therefore,

Perimeter = 3a

P = 3 x 7 = 21cm

Question 2: If the length of parallel sides of a parallelogram is 8cm and 11cm, respectively, then find its perimeter.

Solution:

Given,

Length of parallel sides of a parallelogram is 8cm and 11cm, respectively.

By the formula of perimeter, we know;

Perimeter of Parallelogram = 2(a+b)

P = 2 (8 + 11)

P = 2 x 19

P = 38 cms

Therefore, the perimeter of a given parallelogram is 38 cms.

Question 3: If the radius of a circle is 21cm, then find its perimeter.

Solution: Given,

Radius of circle = 21 cm

We know,

Perimeter of circle = Circumference of circle = 2πr

Therefore,

Circumference = 2 × 22/7 × 21

= 2 × 22 × 3

= 132 cm

Therefore, the perimeter of circle here is equal to 21cm

Question 4: A regular pentagon of side 3cm is given. Find its perimeter.

Solution: Given, length of the side of regular pentagon = 3cm

As we know, a regular pentagon will have all its 5 sides equal.

Hence,

Perimeter of regular pentagon = 5a, where a is the side length

Perimeter = 5 × 3

= 15cm

Therefore, the answer is 15cm here.

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