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.

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

**●** The perimeter of a triangle ABC

= 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.

*The perimeter of the triangle = Sum of the lengths of three 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:**

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:**

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.

**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.

**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

**Word Problems on Perimeter of a Triangle:**

**1.** Two sides of a
triangle are 3 cm and 4 cm. Find the third side of the triangle if its
perimeter is 11 cm.

**Solution:**

First side of the triangle = 3 cm

Second side of the triangle = 4 cm

Perimeter of the triangle = Sum of the lengths of sides

i.e. sum of the lengths of the sides = 11 cm

3 cm + 4 cm + length of the third side = 11 cm

7 cm + length of the third side = 11 cm

But we know that 7 cm + 4 cm = 11 cm (*Note: 11 –
7 = 4*)

Therefore, length of the third side = 4 cm

**Questions and Answers on Perimeter of a Triangle:**

**1.** A triangle has a perimeter of 50 cm. If its two sides
are of lengths 15 cm and 19 cm, what is the length of the third side?

**Answer:** 16 cm

**● ****Related Concepts**

**● ****To
Measure the Length of a Line-segment**

**● ****Examples
on Unit of Mass or Weight**

**● ****Units
for The Measurement of Capacity**

**● ****Examples
on Measurement of Capacity**

**● ****Antemeridian
(a.m.) or Postmeridian (p.m.)**

**● ****Calendar**

**● ****Reading
and Interpreting a Calendar**

**4th Grade Math Activities**

**From Perimeter of a Triangle to HOME PAGE **

**Didn't find what you were looking for? Or want to know more information
about Math Only Math.
Use this Google Search to find what you need.**

## New! Comments

Have your say about what you just read! Leave me a comment in the box below. Ask a Question or Answer a Question.