Example:
For a square with side length 2 m, find its perimeter.
$$
\begin{align}
P &= 4 \times 2\,\text{m} \\[0.5em]
&= 8\,\text{m}
\end{align}
$$
Perimeter of a Polygon
Table Of Contents
🎬 Math Angel Video: How to Calculate Perimeter of Shapes
What is the Perimeter of a Polygon?
⏩️
What is a Polygon?
A polygon is any flat shape with straight sides, like triangles, rectangles, squares, or pentagons.
What is the Perimeter?
The perimeter is the total distance all the way around a shape.
How to Find the Perimeter of a Polygon?
To find the perimeter of a polygon, add up the lengths of all the sides.
🛎️ Finding the Perimeter of a Rectangle
Formula:
$$P = 2 \times (l + w)$$
where $l$ is the length and $w$ is the width.
Example:
For a rectangle with 5 cm length and 3 cm width, find its area.
$$
\begin{align}
P &= 2 \times (5\,\text{cm} + 3\,\text{cm}) \\[0.5em]
&= 2 \times 8\,\text{cm} \\[0.5em]
&= 16\,\text{cm}
\end{align}
$$
🛎️ Finding the Perimeter of a Square
Formula:
$$P = 4 \times s$$ where $s$ is the length of any side.
Perimeter of Triangles
⏩️
Generally, we find the perimeter of a triangle by adding the lengths of all three sides.
🛎️ Perimeter of an Isosceles Triangle:
An isosceles triangle has two equal sides ($a$) and one different side ($b$).
The formula is: $$P = 2a + b$$
- For example, if a triangle has two equal sides of 5 cm and a third side of 3 cm, its perimeter is:
$$
\begin{align}
P &= (2 \times a) + b \\[0.5em]
&= (2 \times 5\,\text{cm}) + 3\,\text{cm} \\[0.5em]
&= 10\,\text{cm} + 3\,\text{cm} \\[0.5em]
&= 13\,\text{cm}
\end{align}
$$
🛎️ Perimeter of an Equilateral Triangle
An equilateral triangle has all three sides of the same length ($a$).
The formula is: $$P = 3a$$
- For example, if all sides of a triangle are 7 cm, find its perimeter:
$$
\begin{align}
P &= 3 \times a \\[0.5em]
&= 3 \times 7\,\text{cm} \\[0.5em]
&= 21\,\text{cm}
\end{align}
$$
How to Find Perimeter of Complex Shapes?
⏩️
The perimeter is the total length around the boundary of a shape, even if the shape isn’t a simple rectangle or square.
🛎 Example: Find the Perimeter of a L-Shaped Figure:
🍪 Quiz: Practise Finding the Perimeter of Polygons
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