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106 LearnersLast updated on December 28, 2025

The perimeter of a shape is the total length of its boundary. The sum of all three sides is called the perimeter of a triangle. Perimeter is also used for fencing a property, sewing, and more. In this topic, we will learn about the perimeter of two triangles.
The perimeter of two triangles is the combined total length of their six sides. By adding the length of all sides from both triangles, we get the total perimeter.
The formula for the perimeter of a single triangle is P = a + b + c , where a , b , and c are the sides of the triangle.
For instance, if two triangles have sides\(ย a_1 = 5, b_1 = 7, c_1 = 9\) and \(a_2 = 4, b_2 = 6, c_2 = 8 \), then their combined perimeter is\( ( P = (5 + 7 + 9) + (4 + 6 + 8) = 39 ).\)
Let’s consider another example of two triangles with side lengths\( ( a_1 = 6, b_1 = 8, c_1 = 10 ) \) and \(( a_2 = 7, b_2 = 9, c_2 = 5 )\).
So the combined perimeter of the two triangles will be: \( P = (6 + 8 + 10) + (7 + 9 + 5) = 45 \).
To find the perimeter of two triangles, we just need to apply the given formula and sum all the sides of both triangles.
For instance, given triangles have sides\( ( a_1 = 3, b_1 = 4, c_1 = 5 ) and ( a_2 = 6, b_2 = 7, c_2 = 8 ).\)
Perimeter = sum of all sides = ( (3 + 4 + 5) + (6 + 7 + 8) = 33 ).
Example
Problem on Perimeter of Two Triangles -
For finding the perimeter of two triangles, we use the formula, \(( P = (a_1 + b_1 + c_1) + (a_2 + b_2 + c_2) )\).
For example, let’s say,\( ( a_1 = 2 \, \text{cm}, b_1 = 3 \, \text{cm}, c_1 = 4 \, \text{cm} ) and ( a_2 = 5 \, \text{cm}, b_2 = 6 \, \text{cm}, c_2 = 7 \, \text{cm} ). \)
Now, the perimeter = sum of all sides = (2 + 3 + 4) + (5 + 6 + 7) = 27 cm .
Therefore, the combined perimeter of the two triangles is 27 cm.


Learning some tips and tricks makes it easier for children to calculate the perimeter of two triangles. Here are some tips and tricks given below:
Did you know that while working with the perimeter of two triangles, children might encounter some errors or difficulties? We have many solutions to resolve these problems. Here are some given below:
Two triangular flower beds have perimeters of 50 inches and 60 inches, respectively. If one of the flower beds is missing a side measuring 18 inches, find the perimeter of both flower beds combined.
The combined perimeter is 110 inches.
Let ‘b’ be the side of the missing side of the first flower bed. And the given perimeter of the first flower bed = 50 inches. One side is missing, and the other two sides are known: 16 inches and 18 inches.
Perimeter of the first triangle = sum of lengths of three sides. 50 = 16 + 18 + b
50 = 34 + b
b = 50 - 34 = 16
Therefore, the missing side is 16 inches. Combined perimeter = 50 + 60 = 110 inches.
A piece of wire 312 inches long is cut into two parts and shaped into two equilateral triangles. Find the length of each side of both triangles if they are equal in size.
52 inches
Given that the total length of the wire is 312 inches, it is shaped into two equilateral triangles of equal size.
Perimeter of each triangle = Total length of the wire divided by 2
Perimeter of each equilateral triangle = \(3 ร a ( 156 = 3 ร a ) ( 156 รท 3 = 52 ) ( a = 52 )\) Therefore, the length of each side of both triangles is 52 inches.
Find the combined perimeter of two equilateral triangles whose sides are 9 cm and 11 cm, respectively.
60 cm
Perimeter of the first triangle = \( 3 \times 9 = 27 cm\)
Perimeter of the second triangle =\( 3 \times 11 = 33 cm \)
Combined perimeter = 27 + 33 = 60 cm
Therefore, the combined perimeter of the two triangles is 60 cm.
Liam is planning two triangular areas for a playground, measuring the sides of the first triangle as 10 meters, 12 meters, and 14 meters, and the second as 8 meters, 15 meters, and 9 meters. How much fencing should Liam buy to go around both areas?
Liam will need 68 meters of fencing to go around both areas.
The perimeter of the first triangle is the sum of all three sides: \( P_1 = 10 + 12 + 14 = 36 \)meters.
The perimeter of the second triangle is the sum of all three sides: \( P_2 = 8 + 15 + 9 = 32 \) meters.
Combined perimeter = \\(P_1 + P_2 = 36 + 32 = 68 \) meters.
Calculate the combined perimeter of two scalene triangular rocks.
Sides of the first triangle are a = 5, b = 12, c = 13
Sides of the second triangle area = 7, b = 9, c = 14
Combined perimeter = (5 + 12 + 13) + (7 + 9 + 14) = 60 meters.
Each side of the scalene triangles has different lengths. The entire distance around both rocks is calculated to be 60 meters by summing the lengths of the sides of both triangles.

Seyed Ali Fathima S a math expert with nearly 5 years of experience as a math teacher. From an engineer to a math teacher, shows her passion for math and teaching. She is a calculator queen, who loves tables and she turns tables to puzzles and songs.
: She has songs for each table which helps her to remember the tables






