Perimeter of a triangle — lesson. Mathematics State Board, Class 6.

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எங்கள் ஆசிரியர்களுடன் 1-ஆன்-1 ஆலோசனை நேரத்தைப் பெறுங்கள். டாப்பர் ஆவதற்கு நாங்கள் பயிற்சி அளிப்போம்

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Now, we shall find the perimeter of a triangle.

Let

$ABC$ be a triangle with sides of length

$a$ ,

$b$ and

$c$

$units$ .

Then, the perimeter of the triangle

$ABC$ is given by:

Perimeter of the triangle

$=$ Sum of the measures of all three sides

Perimeter

$P = AB+BC+CA$

$units$

$P = a+c+b$

$units$

Therefore, the perimeter of the triangle is

$P = a+b+c$

$units$ .

Example:

1. The sides of the triangle are

$7 \ cm$ ,

$8 \ cm$ and

$10 \ cm$ . Find the perimeter of the triangle.

Solution:

Let

$a$ ,

$b$ and

$c$ denote the sides of the triangle. Then,

$a = 7 \ cm$ ,

$b = 8 \ cm$ and

$c = 10 \ cm$ .

Perimeter of the triangle

$=$ Sum of the measures of all three sides

Substituting the values in the formula, we have:

Perimeter,

$P = a+b+c$

$P = 7+8+10$

$cm$

$P = 25 \ cm$

Thus, the perimeter of the triangle is

$25 \ cm$ .

Let us find the perimeter of an equilateral triangle.

A triangle in which all three sides were in the equal length is called the equilateral triangle.

Let

$ABC$ be an equilateral triangle which has sides of length

$a$ units.

We know that the formula to find the perimeter of the triangle is

$P = a+b+c$ , where

$a$ ,

$b$ ,

$c$ are the lengths of three sides of the triangle.

Since for an equilateral triangle, all the sides were equal, then substituting

$a = b = c = s$ in the formula of the perimeter of the triangle, we have:

Perimeter,

$P = s+s+s$

$units$

Therefore, the perimeter of the equilateral triangle is

$P = 3s$ , where

$s$ is the length of three equal sides.

Example:

1. The side length of an equilateral triangle is

$9 \ cm$ . Find the perimeter of an equilateral triangle.

Solution:

The side length of an equilateral triangle is

$s = 9$

$cm$ .

Perimeter

$= 3s$ , where

$s$ is the length of three equal sides.

Substituting the value of

$s$ in the above formula, we have:

Perimeter

$= 3 \times 9$

$cm$

Perimeter

$= 27$

$cm$

Therefore, the perimeter of an equilateral triangle is

$27 \ cm$ .

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4. Perimeter of a triangle

Theory: