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JEE Main 2026 Preparation: Question Papers, Solutions, Mock Tests & Strategy Unacademy » JEE Study Material » Mathematics » Semi Perimeter

Semi Perimeter

The half of a shape's perimeter is referred to as the semi perimeter. The semi perimeter is obtained by dividing the perimeter of a by two.

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In geometry, we may have come across a variety of different types of formulas, such as perimeter, area, height, volume, and other similar terms. When working with polygons, one of the most frequently encountered metrics is the semi perimeter. It is a measurement that is associated with plane figures, which are two-dimensional shapes. Simple formulas can be used to compute the semi perimeter of a variety of various plane figures. In this post, you will discover the definition of semi perimeter, as well as the formula for semi perimeter for various forms, as well as instances of the two terms used.

As we all know, the perimeter of a shape is the distance around it, but the semi perimeter is half the distance around it. The semi perimeter of a given polygon can be computed by dividing its circumference by two for each given polygon. Despite the fact that it is derived from the perimeter in a straightforward manner, the semi perimeter appears frequently in formulas relating to triangles and other shapes, prompting it to be given a separate name. A semi perimeter is represented by the letter “s” in a formula when it is a part of the formula.

 

Semi Perimeter Formula

The formula is Semi perimeter = Perimeter/2.

However, the following table has semi perimeter calculations for a variety of shapes and polygons:

 

Shape

Formula

Explanation

Semi Perimeter of a Triangle formulas

Equilateral triangle

3a/2

a = Length of the side of an equilateral triangle

Isosceles triangle

a + (b/2)

a = Length of congruent sides

b = Length of the third side

Right angle triangle

(base + height + hypotenuse)/2

Height = Perpendicular

Hypotenuse = The longest side

Scalene triangle

(a + b + c)/2

a, b, c are the measures of lengths of three sides

Semi Perimeter of Curved Shapes Formulas

Circle

(2πr)/2 or πr

r = Radius of circle

Semicircle

(πr + 2r)/2

r = Radius of the semicircle

Semi Perimeter of Quadrilaterals Formulas

Rectangle Formula

2(l + b)/2 or l + b

l = Length

b = Breadth

Square

(4a/2) or 2a

a = Side of a square

any quadrilateral

(a + b + c + d)/2

a, b, c, d are the length of sides of the quadrilateral

 

Semi Perimeter of triangle

 

It is possible to calculate the semi perimeter of a triangle by dividing the total perimeter of the triangle by two. Due to the fact that semi’ signifies half, the semi perimeter of a triangle is equal to half the value of the perimeter. In order to determine the area of a triangle using Heron’s formula, the semi perimeter of a triangle must be known. It is possible to express the semi perimeter of a triangle in linear units such as inches, yards, millimetres, and so on. After that, we will go over the formula that is used to calculate the semi-perimeter of a triangular shaped figure. Knowing that the perimeter of a triangle is equal to the sum of the lengths of all its sides, we can calculate its area. Take, for example, a triangle with three equal-length side lengths (a, b and c). The perimeter of the triangle may be computed using this formula: Perimeter = (a+b+c). As a result of using this technique, The semi-perimeter of a triangle is equal to (a + b + c)/2.

 

 

 

Use of the Semi perimeter of Triangle in heron’s formula

When the lengths of all three sides of a triangle are known, the semi perimeter of a triangle can be used to calculate the area of a triangle using Heron’s formula. It is only the lengths of all the triangle’s sides that determine the outcome of this calculation. A semi perimeter is represented by the letter “s,” which is obtained by dividing the perimeter of a triangle by two and is represented by the letter “s.” This is the Heron’s formula, which is written as√[s(s-a)(s-b)(s-c)],  where s denotes the Semi-Perimeter of the triangle and the letters a’, ‘b’, ‘c’ denote the three sides of the triangle. This yields the area of a triangle whose three sides are known in advance of time.

Perimeter of a Semicircle Formula

When calculating the perimeter of a semicircle, the formula for the perimeter of a semicircle is utilised. We must know the diameter or radius of a circle, as well as the length of an arc, in order to solve this problem. In order to get the length of the arc of the semicircle, we must first determine the circumference of a circular figure.

The circumference of a circle is given by the formula C = πd or C = 2πr.

When we take into account the value of C, we can come up with a formula to compute the perimeter of a semicircle, which is determined as the sum of half of a circle’s circumference and the diameter of a circle.

The perimeter of a semicircle is calculated using the formula(πR + d) or (πR + 2R), or R(π + 2)units.

where R = radius of a semicircle

π(pi) is 22/7 or 3.142 and,

d = Diameter of a semicircle.

 Conclusion 

It is possible to calculate the semi perimeter of a triangle by dividing the total perimeter of the triangle by two. Due to the fact that semi’ signifies half, the semi perimeter of a triangle is equal to half the value of the perimeter. In order to determine the area of a triangle using Heron’s formula, the semi perimeter of a triangle must be known.

faq

Frequently asked questions

Get answers to the most common queries related to the JEE Examination Preparation.

What is meant by the term "semi perimeter of triangle"?

Ans. Whenever a triangle has a boundary, the distance around the perimeter fro...Read full

What is indicated by the term "semi-perimeter of a rectangular shape"?

Ans: In geometry, a polygon’s semiperimeter is equal to half of its perimeter, as shown below. Because ...Read full

What is the semi-perimeter of a square?

Ans: As seen in the ‘Smith Diagram’, the semi-perimeter of a squared rectangle is proportional to the nu...Read full

What is the semi-perimeter of a triangle with sides denoted by the letters B and C?

Ans: Semiperimeter =s=2a+b+c

Ans. Whenever a triangle has a boundary, the distance around the perimeter from a vertex to the point on the opposite edge touched by an excircle is equal to the semiperimeter of the triangle. In geometry, a polygon’s semiperimeter is equal to half of its perimeter, as shown below.

Ans: In geometry, a polygon’s semiperimeter is equal to half of its perimeter, as shown below. Because of its straightforward derivation from the perimeter, the semiperimeter appears in enough formulas for triangles and other figures to warrant designation as a separate entity.

 

Ans: As seen in the ‘Smith Diagram’, the semi-perimeter of a squared rectangle is proportional to the number of spanning trees in the rectangle’s semi-perimeter (a planar graph where edges represent squares). The semi-perimeter is represented by a specific number in a specified order, while the square sizes are represented by a different number in the next highest order.

 

Ans: Semiperimeter =s=2a+b+c

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