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Geometry and Measurement Videos 88 videos

SAT Math 1.1 Geometry and Measurement
719 Views

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

SAT Math 1.2 Geometry and Measurement
246 Views

SAT Math: Geometry and Measurement Drill 1, Problem 2. If A = (0, 4), B = (-3, 2), and C = (1, 0), which point is in the interior of angle ABC?

SAT Math 2.3 Geometry and Measurement
267 Views

SAT Math 2.3 Geometry and Measurement. Find the length of AB.

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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?

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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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