Perimeter of Triangle

The sum of the lengths of the sides is the perimeter of any polygon. In the case of a triangle,

Perimeter = Sum of the three sides.

Always include units in the final answer. If the sides of the triangle are measured in centimeters then the final answer should also be in centimeters.

Formula for Perimeter of Triangle: The formula for the perimeter of a closed shape figure is usually equal to the length of the outer line of the figure. Therefore, in the case of a triangle, the perimeter will be the sum of all three sides. If a triangle has three sides A, B, and C, then,

Perimeter, X = A + B + C, If A, B, and C are the side measures, and X is the perimeter.

Scalene Triangle: If a triangle has all three sides of different lengths, it is called a scalene triangle.

Perimeter of Scalene triangle: It can be calculated by finding the sum of all the unequal sides.

Hence, Perimeter = a + b + c, where "a", "b", and "c" are the different sides.

Isosceles Triangle: If a triangle has two sides of equal length, it is an isosceles triangle.

Perimeter of Isosceles triangle: The perimeter of an isosceles triangle can be calculated by finding the sum of the equal and unequal sides.

Hence, Perimeter = 2a + b where, a = sides of equal length and b = the third side (unequal side)

Equilateral Triangle: If a triangle has all the sides of equal measure, it is called an equilateral triangle.

Perimeter of Equilateral Triangle: $small 3times a$ where a = length of each side of the triangle.

Right Triangle: A triangle that has one of the angles as $small 90^{0}$ is called a right-angled triangle or a right triangle.

Perimeter of Right Triangle: Its perimeter can be calculated by adding the given sides.

Hence, Perimeter = a + b + c

Isosceles Right Triangle: A right triangle with two equal sides and two equal angles is called an isosceles right triangle.

Perimeter of Isosceles Right Triangle: Its perimeter can be calculated by adding the given sides.

Hence, Perimeter = 2l + h where, l = length of the equal side and h = length of the third side

Illustration: Find the perimeter of a triangle having two equal sides of measure 7 cm and one unequal side of measure 6 cm.

Solution: As we know that If a triangle has two sides of equal length, it is an isosceles triangle. Also, we know that the Perimeter of isosceles triangle = 2a + b

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Sample Questions

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Question : 1

If perimeter of a triangle is 35 cm and length of two sides of triangle are 5 cm, 10 cm then calculate the length of third side of triangle .
A. 10 cm	B. 20 cm	C. 13 cm	D. 11 cm
Right Option : B
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Question : 2

Find the perimeter of a triangle if the three sides have measures 10 cm, 5 cm, 1.5 cm respectively.
A. 15.9 cm	B. 12 cm	C. 16.5 cm	D. 16 cm
Right Option : C
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