# Circles: Radius, Diameter, Circumference And Pi | Geometry | Khan Academy

A circle is at the foundation of geometry and how its parts relate to each other is both completely logical and a wonder.

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Geometry on Khan Academy: We are surrounded by space. And that space contains lots of things. And these things have shapes. In geometry we are concerned with the nature of these shapes, how we define them, and what they teach us about the world at large–from math to architecture to biology to astronomy (and everything in between). Learning geometry is about more than just taking your medicine (“It’s good for you!”), it’s at the core of everything that exists–including you. Having said all that, some of the specific topics we’ll cover include angles, intersecting lines, right triangles, perimeter, area, volume, circles, triangles, quadrilaterals, analytic geometry, and geometric constructions. Wow. That’s a lot. To summarize: it’s difficult to imagine any area of math that is more widely used than geometry.

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## 21 thoughts

1. Tima Pustovit says:

#CS:GOcros

2. Ashraf pathaan says:

lol sal sounds like he is recording from under the ocean with that hilarious voice of his. 😉

3. musab qaiser says:

thx really helped in exams

4. Alvin Dueck says:

so, you can have the pi. you just can’t eat it :'(

5. Alvin Dueck says:

Ok. How would you get the circumference of an oval

6. Sainsburys Basic Bleach says:

Circle song is bæ

7. youssef Kachmar says:

this is really gonna help me get in to the high school i wanna go to

8. Satomi August says:

pause at 0:35 there you will see a nipple

9. harry jhons says:

pie delicious ymmmmmmmmmmmmmm

10. harry jhons says:

jk

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12. Kawaii PandaJoy says:

it really helped me catch up when I’m absent at school coz I’m always ill

13. Jordan West says:

cool

14. PurpleGemstone says:

thanks man! i have an exam tomorrow 😀 LIKED!

15. tomasangelicus says:

how I can solve it

16. Panther5050 says:

Sup guys say the first 100 digit of PI (3.14159……………………………………………………..)

17. Ifinity_Blitzer _Master says:

you are literally the greatest person alive. You saved me from a F in my math class

18. Brandon Brinker says:

thx this helped alot

19. APp Cuber says:

3.14159265358979323846264338327950288419716939937510582097494459230781640628620899862803482534211706798214808651328230664709384460955058223172535940812848111745028410270193852110555964462294895493038196442881097566593344612847564823378678316527120190914564856692346034861045432664821339360726024914127372458700660631558817488152092096282925409171536436789259036001133053054882046652138414695194151160943305727036575959195309218

20. This is not Click bait says:

that realy helped thanks