Perimeter of a Triangle
In this lesson, we will learn about the perimeter of a triangle...
About This Lesson
In this lesson, we will:
- Learn about the formula for the perimeter of a triangle.
- See an example on using the formula to find a triangle's perimeter.
- See another example on using the formula to find the side length of a triangle.
The study tips and math video below will explain more.
The triangle shown on the right has the side lengths of a, b and c. Its perimeter, P, will be the sum of all the side lengths. Hence:
P = a + b + c
The math video below will give more explanation on this. Also, we will see some examples on how to use this formula.
Video on the perimeter of a triangle
Math Video Transcript
In this lesson, we will learn about the perimeter of a triangle.
Consider this triangle. This triangle has the side lengths of ‘a’, ‘b’ and ‘c’.
Now, to find the perimeter of this triangle, P, we just add the length of these sides together.
Hence, we have ‘a’ plus 'b' and finally, plus 'c'.
Therefore, the perimeter, 'P', of a triangle, is equals to a + b + c.
Note that, in any calculation, when we found the value of 'P', it is important to include the unit.
For example, if 'a', ‘b', and 'b' are given in centimeter, the unit for the perimeter will be in centimeter as well.
The next video will show some examples on using this formula.
Video on the examples on using the formula P=a+b+c
Math Video Transcript
After understanding the basics behind the perimeter of a triangle, let's see some examples on it.
Find the perimeter of this triangle, when its side lengths are 3cm, 4cm, and 5cm.
We start with the formula for the perimeter of a triangle, 'P', equals to a + b + c.
One of the sides is given as 3cm. Hence, we can substitute 'a' with 3.
Similarly, we can substitute 'b' with '4', and substitute 'c' with, 5.
Let's simplify this. 4 add with 5, gives 9. 3 add with 9, gives 12.
Now, we have 'P' equals to 12.
Note that, this number has no meaning, unless we include the unit for it.
Since these lengths are given in centimeter, the unit for the perimeter will also be in centimeter.
Therefore, the perimeter of this triangle is equals to 12 centimeter.
Next example, the perimeter of this triangle, is 21ft. Its side lengths are 7ft, 9ft, and x feet. Find x.
Again, we start with the formula for the perimeter of a triangle, 'P' equals to, a + b + c.
Since the perimeter is given as 21ft, we can substitute 'P' with 21.
Now, the length of one of the side is given as x. Hence we can substitute ‘a’ with x.
Similarly, we can substitute 'b' with 7, and 'c' with 9.
We can simplify this equation, by adding 7, with 9. This gives 16.
Now, we have, x + 16, equals to, 21.
Let's rewrite this, so that it will look neater.
Here, note that, to find x, we need to remove 16.
We can do so, by adding -16, to both sides of the equation. Hence, we get, x equals to, 21 minus 16.
21, minus 16, give 5.
Now, we have x, equals to 5. Note that, it is important to include the unit.
From here, it is obvious that, we have 5 feet.
Finally, x = 5 feet.
That is all for this lesson. Try out the practice question to further your understanding.
Practice Questions & More
Multiple Choice Questions (MCQ)
Now, let's try some MCQ questions to understand this lesson better.
You can start by going through the series of questions on the perimeter of a triangle or pick your choice of question below.
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