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Playlist Circles 22 videos

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Attributes of Circles
6371 Views

This video can run circles around other videos about circles. Sir Cumference, of Round Table fame, explains all the properties of… well, circles....

1
Perimeter and Circumference
10658 Views

It's super useful to be able to find the distance around stuff. Like when you’re being pursued by authorities while running around the base of an...

2
Area of a Sector
2665 Views

Time to learn about the area of a sector. And no, that's not the sector's bedroom with a bumper sticker on the door that reads, "GO AWAY."

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SAT Math 1.1 Geometry and Measurement 719 Views


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Description:

SAT Math 1.1 Geometry and Measurement. What is the circumference of the circle?

Language:
English Language

Transcript

00:03

Here’s a question that's part of a balanced Shmoopy breakfast.

00:06

A circle has an area of 100π cm2. What is the circumference of the circle?

00:13

And here are the potential answers...

00:16

All right…seems to us we’re going to have to know a formula or two to solve this puppy.

00:24

We should know that the area of a circle is πr2…

00:26

…and that the circumference of a circle is 2πr.

00:31

The problem has graciously told us the area, so we should be able to figure out what r is,

00:35

and then just plug ‘er into the circumference formula.

00:38

Okay…so by swapping out what we’re given with what we know…

00:41

…we get that 100π equals πr2.

00:44

We can divide pi out of both sides to give us 100 equals r squared…and then take the

00:48

square root of both sides to get r = 10.

00:51

All right, we can take our new r value and move it over to the circumference formula…

00:56

…which becomes 2 pi times 10…or 20 pi.

00:59

Which is answer D.

01:00

Wow…20 pi… that’s not just a pi… that’s a whole bakery.

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