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Perimeter: introduction

Perimeter is a math concept that measures the total length around the outside of a shape. To find the perimeter, you add together the lengths of all the sides. This works for any shape, including triangles, rectangles, pentagons, and even irregular polygons. Created by Sal Khan.

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  • starky seedling style avatar for user Kokona Aishi
    Do 3 dimension objects like cubes have perimeter?
    (22 votes)
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  • hopper jumping style avatar for user #dibs colick
    what is a meaning of gnus
    (11 votes)
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  • aqualine ultimate style avatar for user Smile at something every day
    This is strange but why is sometimes the perimeter bigger than the area
    (8 votes)
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  • blobby green style avatar for user adaobowu.CU
    perimeter in mixed fractions
    (8 votes)
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  • aqualine ultimate style avatar for user Smile at something every day
    Also, if you multiply a fraction by a whole number when doing area, it might become smaller than the perimeter
    (5 votes)
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  • female robot grace style avatar for user Loren997
    Why do you have to add up all the three sides?
    (5 votes)
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  • blobby green style avatar for user Blen Mesfin Gebremichael
    what is perimeter
    (4 votes)
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    • female robot ada style avatar for user Norah J
      Perimeter is the outside length/measurement of the shape. (For example, if a square's singulair side length is 2m, that you would add: 2+2+2+2= 8 to get the perimeter - since perimeter is the the path that surrounds the shape. I'm not sure if this makes it more confusing for you, but I hope it helps.)
      (1 vote)
  • blobby green style avatar for user uoer99
    Can someone help me with alrealdy knowing the premiter but dont know the length is missing?
    (4 votes)
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  • old spice man green style avatar for user daena.simpson
    For example, you have a square court and you want to know the length of each side but you want to put your answer in a mixed number or a decimal what would you do?
    (4 votes)
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  • piceratops ultimate style avatar for user Nikko Rojas :)
    according to mr.khan
    When people use the word "perimeter" in everyday language, they're talking about the boundary of some area. And when we talk about perimeter in math, we're talking about a related idea. But now we're not just talking about the boundary. We're actually talking about the length of the boundary. How far do you have to go around the boundary to essentially go completely around the figure, completely go around the area? So let's look at this first triangle right over here. It has three sides. That's why it's a triangle. So what's its perimeter? Well, here, all the sides are the same, so the perimeter for this triangle is going to be 4 plus 4 plus 4, and whatever units this is. If this is 4 feet, 4 feet and 4 feet, then it would be 4 feet plus 4 feet plus 4 feet is equal to 12 feet. Now, I encourage you to now pause the video and figure out the parameters of these three figures. Well, it's the exact same idea. We would just add the lengths of the sides. So let's say that these distances, let's say they're in meters. So let's say this is 3 meters, and this is also 3 meters. This is a rectangle here, so this is 5 meters. This is also 5 meters. So what is the perimeter of this rectangle going to be? What is the distance around the rectangle that bounds this area? Well, it's going to be 3 plus 5 plus 3 plus 5, which is equal to-- let's see, that's 3 plus 3 is 6, plus 5 plus 5 is 10. So that is equal to 16. And if we're saying these are all in meters, these are all in meters, then it's going to be 16 meters. Now, what about this pentagon? Let's say that each of these sides are 2-- and I'll make up a unit here. Let's say they're 2 gnus. That's a new unit of distance that I've just invented-- 2 gnus. So what is the perimeter of this pentagon in gnus? Well, it's 2 plus 2 plus 2 plus 2 plus 2 gnus. Or we're essentially taking 1, 2, 3, 4, 5 sides. Each have a length of 2 gnus. So the perimeter here, we could add 2 repeatedly five times. Or you could just say this is 5 times 2 gnus, which is equal to 10 gnus, where gnu is a completely made-up unit of length that I just made up. Here we have a more irregular polygon, but same exact idea. How would you figure out its perimeter? Well, you just add up the lengths of its sides. And here I'll just do it unitless. I'll just assume that this is some generic units. And here the perimeter will be 1 plus 4 plus 2 plus 2-- let me scroll over to the right a little bit-- plus 4 plus 6. So what is this going to be equal to? 1 plus 4 is 5, plus 2 is 7, plus 2 is 9, plus 4 is 13, plus 6 is 19. So this figure has a perimeter of 19 in whatever units these distances are actually given.
    (4 votes)
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Video transcript

When people use the word "perimeter" in everyday language, they're talking about the boundary of some area. And when we talk about perimeter in math, we're talking about a related idea. But now we're not just talking about the boundary. We're actually talking about the length of the boundary. How far do you have to go around the boundary to essentially go completely around the figure, completely go around the area? So let's look at this first triangle right over here. It has three sides. That's why it's a triangle. So what's its perimeter? Well, here, all the sides are the same, so the perimeter for this triangle is going to be 4 plus 4 plus 4, and whatever units this is. If this is 4 feet, 4 feet and 4 feet, then it would be 4 feet plus 4 feet plus 4 feet is equal to 12 feet. Now, I encourage you to now pause the video and figure out the parameters of these three figures. Well, it's the exact same idea. We would just add the lengths of the sides. So let's say that these distances, let's say they're in meters. So let's say this is 3 meters, and this is also 3 meters. This is a rectangle here, so this is 5 meters. This is also 5 meters. So what is the perimeter of this rectangle going to be? What is the distance around the rectangle that bounds this area? Well, it's going to be 3 plus 5 plus 3 plus 5, which is equal to-- let's see, that's 3 plus 3 is 6, plus 5 plus 5 is 10. So that is equal to 16. And if we're saying these are all in meters, these are all in meters, then it's going to be 16 meters. Now, what about this pentagon? Let's say that each of these sides are 2-- and I'll make up a unit here. Let's say they're 2 gnus. That's a new unit of distance that I've just invented-- 2 gnus. So what is the perimeter of this pentagon in gnus? Well, it's 2 plus 2 plus 2 plus 2 plus 2 gnus. Or we're essentially taking 1, 2, 3, 4, 5 sides. Each have a length of 2 gnus. So the perimeter here, we could add 2 repeatedly five times. Or you could just say this is 5 times 2 gnus, which is equal to 10 gnus, where gnu is a completely made-up unit of length that I just made up. Here we have a more irregular polygon, but same exact idea. How would you figure out its perimeter? Well, you just add up the lengths of its sides. And here I'll just do it unitless. I'll just assume that this is some generic units. And here the perimeter will be 1 plus 4 plus 2 plus 2-- let me scroll over to the right a little bit-- plus 4 plus 6. So what is this going to be equal to? 1 plus 4 is 5, plus 2 is 7, plus 2 is 9, plus 4 is 13, plus 6 is 19. So this figure has a perimeter of 19 in whatever units these distances are actually given.