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SAT Math 1.1 Geometry and Measurement. What is the circumference of the circle?
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. Find the length of AB.
SAT Math 1.1 Geometry and Measurement 719 Views
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SAT Math 1.1 Geometry and Measurement. What is the circumference of the circle?
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…
Full Transcript
- 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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