The perimeter indicates the distance we will walk if we start from a certain point, complete a full lap, and return exactly to the starting point. For example, if we are asked what the perimeter of the waist is, we will take a tape measure and measure the perimeter from a certain point until completing a full lap and returning to the same point from which we started the measurement. It works exactly the same way in mathematics. The perimeter of any shape is the distance from a specific point back to it after having completely surrounded it. If this is our figure:

Its perimeter will be the distance we cover if we travel along its line from a certain point, and return to it after making a full lap. Imagine that you are surrounding the figure:

The perimeter is measured in units of mm, cm, or meters, according to what the question states. Generally, most figures are given in units of cm. We can convert the different units of measure in the following way: $1$ cm = $10$ mm $1$ meter = $100$ cm

Now we will learn to calculate the perimeter of the most known figures. Are we ready? How is the perimeter calculated in general? All the lengths of the edges (or sides) of the figure are added together. The sum of all the edges is the perimeter.

Perimeter of the Square

$a$ -> Side of the square In the square, all sides are equal, therefore, its perimeter will be $4$ times the side $a$. We will multiply the side of the square by $4$.

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Let's add up the sides of the rectangle. The opposite sides are equal.

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Perimeter of the triangle

Let's add up all the sides of the triangle. In an isosceles triangle it is enough to know the length of the base and one of the two equal sides. In an equilateral triangle it is enough to know the length of one side.

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The key to calculating the perimeter of these figures is to add up absolutely all the sides without forgetting any of them. Start on one side, follow the entire round and stop when you reach the same side from which you started.