What I want to do in this video

is a fairly straightforward primer on perimeter and area. And I’ll do perimeter

here on the left, and I’ll do area

here on the right. And you’re probably pretty

familiar with these concepts, but we’ll revisit it

just in case you are not. Perimeter is

essentially the distance to go around something

or if you were to put a fence around

something or if you were to measure– if you were to

put a tape around a figure, how long that tape would be. So for example, let’s

say I have a rectangle. And a rectangle is a figure that

has 4 sides and 4 right angles. So this is a

rectangle right here. I have 1, 2, 3, 4 right angles. And it has 4 sides,

and the opposite sides are equal in length. So that side is going to be

equal in length to that side, and that side is equal

in length to that side. And maybe I’ll label the

points A, B, C, and D. And let’s say we

know the following. And we know that

AB is equal to 7, and we know that

BC is equal to 5. And we want to know, what

is the perimeter of ABCD? So let me write it down. The perimeter of

rectangle ABCD is just going to be equal to the sum

of the lengths of the sides. If I were to build a fence, if

this was like a plot of land, I would just have

to measure– how long is this side

right over here? Well, we already know

that’s 7 in this color. So it’s that side right

over there is of length 7. So it’ll be 7 plus

this length over here, which is going to be 5. They tell us that. BC is 5. Plus 5. Plus DC is going to

be the same length is AB, which is

going to be 7 again. So plus 7. And then finally, DA a or AD,

however you want to call it, is going to be the same length

as BC, which is 5 again. So plus 5 again. So you have 7 plus 5 is 12

plus 7 plus 5 is 12 again. So you’re going to

have a perimeter of 24. And you could go the

other way around. Let’s say that you

have a square, which is a special case

of a rectangle. A square has 4 sides and 4 right

angles, and all of the sides are equal. So let me draw a square here. My best attempt. So this is A, B, C, D. And

we’re going to tell ourselves that this right

here is a square. And let’s say that this

square has a perimeter. So square has a perimeter of 36. So given that, what is the

length of each of the sides? Well, all the sides are going

to have the same length. Let’s call them x. If AB is x, then BC is x,

then DC is x, and AD is x. All of the sides are congruent. All of these segments

are congruent. They all have the same

measure, and we call that x. So if we want to figure

out the perimeter here, it’ll just be x plus x

plus x plus x, or 4x. Let me write that. x

plus x plus x plus x, which is equal to 4x, which

is going to be equal to 36. They gave us that

in the problem. And to solve this, 4

times something is 36, you could solve that

probably in your head. But we could divide

both sides by 4, and you get x is equal to 9. So this is a 9 by 9 square. This width is 9. This is 9, and then the height

right over here is also 9. So that is perimeter. Area is kind of a

measure of how much space does this thing take

up in two dimensions? And one way to think about area

is if I have a 1-by-1 square, so this is a 1-by-1 square–

and when I say 1-by-1, it means you only have

to specify two dimensions for a square or a rectangle

because the other two are going to be the same. So for example, you could

call this a 5 by 7 rectangle because that immediately

tells you, OK, this side is 5 and that side is 5. This side is 7,

and that side is 7. And for a square, you could

say it’s a 1-by-1 square because that specifies

all of the sides. You could really say,

for a square, a square where on one side is 1,

then really all the sides are going to be 1. So this is a 1-by-1 square. And so you can view

the area of any figure as how many 1-by-1 squares

can you fit on that figure? So for example, if we were going

back to this rectangle right here, and I wanted to find out

the area of this rectangle– and the notation

we can use for area is put something in brackets. So the area of rectangle

ABCD is equal to the number of 1-by-1 squares we can

fit on this rectangle. So let’s try to do

that just manually. I think you already

might get a sense of how to do it a little bit quicker. But let’s put a bunch of 1-by-1. So let’s see. We have 5 1-by-1 squares

this way and 7 this way. So I’m going to try my

best to draw it neatly. So that’s 1, 3, 3,

4, 5, 6, and then 7. 1, 2, 3, 4, 5, 6, 7. So going along one of the

sides, if we just go along one of the sides like

this, you could put 7 just along one side just like that. And then over here,

how many can we see? We see that’s 1 row. And that’s 2 rows. Then we have 3 rows and

then 4 rows and then 5 rows. 1, 2, 3, 4, 5. And that makes sense because

this is 1, 1, 1, 1, 1. Should add up to 5. These are 1, 1, 1, 1, 1, 1, 1. Should add up to 7. Yup, there’s 7. So this is 5 by 7. And then you could

actually count these, and this is kind of straight

forward multiplication. If you want to know the

total number of cubes here, you could count it, or you can

say, well, I’ve got 5 rows, 7 columns. I’m going to have 35–

did I say cube– squares. I have 5 squares in this

direction, 7 in this direction. So I’m going to have

35 total squares. So the area of this figure

right over here is 35. And so the general

method, you could just say, well, I’m just going to

take one of the dimensions and multiply it by

the other dimension. So if I have a

rectangle, let’s say the rectangle is

1/2 by 1/2 by 2. Those are its dimensions. Well, you could

just multiply it. You say 1/2 times 2. The area here is going to be 1. And you might say, well,

what does 1/2 mean? Well, it means,

in this dimension, I could only fit 1/2

of a 1-by-1 square. So if I wanted to do

the whole 1-by-1 square, it’s all distorted here. It would look like that. So I’m only doing half of one. I’m doing another half

of one just like that. And so when you add this

guy and this guy together, you are going to

get a whole one. Now what about area of a square? Well, a square is

just a special case where the length and

the width are the same. So if I have a square–

let me draw a square here. And let’s call that XYZ– I

don’t know, let’s make this S. And let’s say I wanted

to find the area and let’s say I know

one side over here is 2. So XS is equal to 2, and I

want to find the area of XYZS. So once again, I

use the brackets to specify the area of this

figure, of this polygon right here, this square. And we know it’s a square. We know all the sides are equal. Well, it’s a special

case of a rectangle where we would multiply the

length times the width. We know that they’re

the same thing. If this is 2, then

this is going to be 2. So you just multiply 2 times 2. Or if you want to

think of it, you square it, which is

where the word comes from– squaring something. So you multiply 2 times 2,

which is equal to 2 squared. That’s where the

word comes from, finding the area of a

square, which is equal to 4. And you could see

that you could easily fit 4 1-by-1 squares

on this 2-by-2 square.

nice one i understood nicely in once …..

Good job

You heló me So much thanks

Lit hacks

I am such an idiot I don't

understand 😭😭 I need an easier way 😢

You tought me many anithing ku5a khan thank you your so smart

Thx so much I have a test on this tomorow and I’m sure I will get a good grade!

I love math

DC

I love it

your dope

What software is this

This help me to think good

I understood very much

👎

Please be my teacher.

Thanks helped me a lot

goooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooodddddddddddddddddddddddddddddddddddddddddd

D

Didn’t work

your a great teacher, but you forgot to put cm, m, dm, km,

montone

thx man you helped my grade improve

This is a good video

thank you you are awsome

yoo person i have a test tomorrow thanks this vid heps alot:D

This is super helpful, I used to be able to do this but I always manage to forget the simplest things especially under the pressure of a time limit and all. I need to start train in my memory and this video did a great job at reminding me, thanks so much.

Thank you

.

test tomorrow

opens khan academy playlistTYSM My math SOL is today and I'm not well with this skill

Not helpful

khan academy's channel is better than Dantdm

Do u use ur hand or the mouse?

i liked the video

thaaaaaaannnnnkkkkkk yyooouuuuu god bless u

Lets just hope this helps me get a good grade for my first report card, and 8th grade six flags event

Your way better than my teacher

Can you please let me know what tablet is used to make videos like this?

Exelty

This isn't really helping me in my situation. My homework is SUPER complicated. I can't understand it.

I am in 4th grade and I taught myself this 1 – 2 years ago. This really helped me review though. Thanks a ton!

👧🏻

👚

👖

BTW

Find the differences…

1.

Level : Easy

🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦐🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑🦑

🐳🐳🐳🐳🐳🐳🐳🐳🐳🐋🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳🐳

Level : Medium

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Level : Hard

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OOF… my fingers hurt from typing.

This helped me sooo much!

Thank you

i disliked this video useless

mincraft

भाषा हिन्दी रख

Thanks u saved me 😀😀

Cc do a video about area

2:19 is not the correct answer

Perimeter of a rectangle is not a+b+c+d

It’s 2base + 2height

i am in 3grade

I need to study for the QUIZ BEE!!!! 😰😰😰😰😰😰😰😰😰😰😰😰AND IM GRADE 4

THANK you sensei thank you so very much 🤩🤩👩🎤👩🎨👰🧝♀️

you helped me pass my test

I am in grade 5 i love your explanig but i love bright colores becase put on the bored black😑

I have to do my homework and then watch Khan academy for an hour

super

YOUR WELCOME

I STILL DONT GET IT DO

UGH!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I love it

That was a nice nice video

Moral of the story in the perimeters add all the angles in the area multiply both angles thank me later 😉

good gob

this is amazing

my favourite subject

I’m reading the comments instead of learning.Im grade 2 and im learning this my homework

you saved my life tomorrow i have a test

Omg this helped soo much thank you so much

I’m so grateful for you vids

Thank you dude I had a test tomorrow and I got on question wrong

hi

I am so bored on hearing your math stuffs

nice

this is okay

It's good but why the black baground sir

You’re so good at maths

My savior

Thank you mr. khan! This is really helpful!

Thanks, god i was feeling real dumb xD

Fast and simple explanation

You made this seem like calculus too much. Where are the formulas ?

Yass! This helped so much. I sub.

I love this I am in 5grade and this help me a lot thank you

omg your da best khan you should become a teacher no something better

People are here cause ur teacher doesn't know how to do her job or because ur reversing for a test

KHAN ACADEMY BETTER THAN MY MATH TEACHER/MOM/DAD teaching me omggggg lets get them more subs

Beautiful writing

OMG MORE HELPFUL BUT SOMETIMES CONFUSING 😓😓😓😎

my math teacher brought me here

OMG

Because of your voice each or every question seem to be very easy

this was hard btw it turend easy

What about taking the Area of a rectangle? Help me please

Nice

Sir thanks

I got 98 because of khan academy

I Subbed

thank u this help me alot ur awesome

you forgot the units

Bro if you we're my teatcher I would get all A dude

In year 8, I have a test in 3 days..I’ll tell you if I get high marks!

What about irregular shapes

I will tell if I got hi grade on my exam thank you😊😊