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## Class 7 (Foundation)

### Course: Class 7 (Foundation)>Unit 8

Lesson 1: Variables

# Perimeter of a square using variables

Let's learn how to write the perimeter for any square in the language of mathematics using variables. Created by Aanand Srinivas.

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• Is that the same with a rectangle
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## Video transcript

in this video I want to talk about variables in common rules variables something that's new for you in things that are old in common rules like perimeter of a square perimeter of a rectangle things that you already know let's bring this new idea in them now why should we do this we're doing this because variables can be a little hard to understand or use at first I I in fact remember being in school and being afraid of these things because it first started I think my book was filled with beautiful numbers five ten fifteen or maybe even big numbers but nothing was very scary and all of a sudden I remember my book being filled with alphabets XY and XY squared said or something like that and I began to get a little skin if I see a page which has only these kind of alphabets in it may be all written all over the page then I won't even feel like reading that page and then I learned that these alphabets in math when we used them they used as variables and so that's a word that I learned variables and it took me some time to understand that variable is just a big word this word variable it's just a big word for saying any number any number so best the best way to understand why a variable means any number is to look at examples let's look at that the first example we look at is that of perimeter of a square very meter of a square and to do this let's imagine that you own a fence shop in a village I'm gonna imagine when you'll want to use variables so let's say you own this fence shop and then now people come to you and they want fences and they say the first person comes to you and says I have a field of side the square field of sight five meters and you say okay the fence length you need is five five five five four fives or four into five meters and he is happy you give him 20 meters of fence and they go away the next person comes to you and they say I have a oh I have a field of of size seven meters and it's also a square how much do I need and you say okay seven dozen it's four times seven seven plus seven plus seven plus seven another person comes to you and then now you begin to get a little tired because it is happening over months and months he does you have 27 meters and you say it does not matter again what your length is does not matter it will still be four times 27 that's the amount of fence you need so after doing this for a while maybe you get like really lazy to do all these calculations so you tell him hey listen I do not care what the size of your field is it can be any length any length does not matter as long as it's a square just do one thing just take four and multiply it with your any length and tell me how much fence you want don't keep asking me so four into any length you know is going to give you your perimeter which is the length of the fence you need perimeter is just another word for how much fence length you need so you can see that whether it's 4 into 5 or 4 into 7 or 4 into 27 does not really matter so 4 times any length is perimeter and maybe after some time you you get a little lazy to write this down so you write 4 into L and what is this L really stand for any length equals perimeter and you want to write P with us perimeter is too long so this looks much smaller crisp and easy to write a long sentence in English if you have a square field and if it's length is anything it does not matter just multiply that with 4 and you'll get the amount of fence length or perimeter you need look at the length of that sentence and that much has been compressed made small into this sentence over here if you write it like this then you're using what's called a variable now why are you using this variable because it's easier than telling this big sentence and what does this variable really stand for just any length L here just stands for a squares length which can be any length this still works and P stands for the perimeter of that square now I want you to try and do the same thing for a rectangular field if the field was a rectangle can you write what the perimeter will be in variables