Perimeter of a Triangle

We will discuss here how to find the perimeter of a triangle. We know perimeter of a triangle is the total length (distance) of the boundary of a triangle.

Perimeter of a triangle is the sum of lengths of its three sides.

Perimeter of a Triangle

For example, perimeter of the ∆PQR = PQ + QR + RP

The perimeter of a triangle ABC

Perimeter of a Triangle

                    = AB + BC + CA

                    = 2 cm + 4 cm + 3 cm,

(add the length of each side of the triangle).

                     = 9 cm

Perimeter of the triangle = Sum of the sides.


Let us consider some of the examples on perimeter of a triangle:

1. Find the perimeter of a triangle having sides 3 cm, 8 cm and 6 cm.

Solution:

Examples on Perimeter of a Triangle

Perimeter of a triangle

                   = Sum of all the three sides

                   = AB + BC + AC

                   = 3 cm + 8 cm + 6 cm

                   = 17 cm


2. Find the perimeter of the triangle PQR whose sides are 4 cm, 6 cm and 8 cm.

Solution:

Perimeter of Triangle

In the figure PQ = 4 cm, PR = 6 cm and QR = 8 cm

The perimeter of the rectangle PQR

= 4 cm + 6 cm + 8 cm

= 18 cm


3. Find the perimeter of an equilateral triangle whose one side is 5 cm.

Solution:

A triangle in which all the sides are equal is called an equilateral triangle.

Perimeter of the equilateral triangle = 3 × side

                                                    = 3 × 5 cm

                                                    = 15 cm

Thus, perimeter = 15 cm.


4. Find the perimeter of a triangle whose length of three sides are 8 cm, 11 cm, 13 cm.

Solution:

To find the perimeter of the triangle, we add all the sides together.

Perimeter of a triangle

                  = Sum of all the three sides

                  = 8 cm + 11 cm + 13 cm

                  = 32 cm


5. Find the perimeter of a triangle whose sides are 5 cm, 2 cm and 3 cm.

Solution:

Perimeter of the triangle is the sum of the lengths of its sides.

Perimeter = 5 cm + 2 cm + 3 cm

Thus, perimeter = 10 cm.


6. Find the perimeter of each triangle.

Find the Perimeter of each Triangle

Solution: 

(i) Perimeter of ∆XYZ = 5.5 cm + 6 cm + 6 cm = 17.5 cm

(ii) Perimeter of ∆ABC = 8 cm + 6 cm + 6 cm = 20 cm

(iii) Perimeter of ∆PQR = 4 cm + 3 cm + 5 cm = 12 cm


7. Find the perimeter of the given shapes.

Find the Perimeter of the given Shapes

Solution:

(i) Perimeter = PQ + QR + RS + ST + TU + UV + VP

                   = 2.5 cm + 3 cm + 2 cm + 3 cm + 2.5 cm + 4 cm + 4 cm

                   = 21 cm


(ii) Perimeter = PQ + QR + RS + SP

                    = 4 cm + 4 cm + 4 cm + 4 cm

                    = 16 cm


(iii) Perimeter = PQ + QR + RS + ST + TP

                     = 7 cm + 6 cm + 4 cm + 3 cm + 5 cm

                     = 25 cm

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