This may not sound very smart but why did you multiple 3*3

Sal multiplied 3 and 3 because the formula for getting area is A = r^2 pi. If our radius is 3, and if part of the formula is r^2, to get the radius to the second power you multiply 3 and 3 .

at 1:05 what was that green thing

It is due to an incomplete answer. Once you finish typing your answer, assuming it is an acceptable form for the particular question, the green guy goes away:)

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Class 10 (Marathi)

Course: Class 10 (Marathi) > Unit 11

Lesson 6: Areas of combination of plane figures

Area of a shaded region

Name: Area of a shaded region
Uploaded: 2013-10-26T05:47:24Z
Description: Here's a fun one: find the area of a shaded region where you first determine the area of a square and then the area of a circle.

CCSS.Math:

7.G.B.4

Google Classroom

Here's a fun one: find the area of a shaded region where you first determine the area of a square and then the area of a circle. Created by Sal Khan.

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Sydney
Posted 7 years ago. Direct link to Sydney's post “This may not sound very s...”
This may not sound very smart but why did you multiple 3*3
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(14 votes)
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- Daniel Hancock
  Posted 7 years ago. Direct link to Daniel Hancock's post “Sal multiplied 3 and 3 be...”
  Sal multiplied 3 and 3 because the formula for getting area is A = r^2 pi. If our radius is 3, and if part of the formula is r^2, to get the radius to the second power you multiply 3 and 3 .
  Comment on Daniel Hancock's post “Sal multiplied 3 and 3 be...”
  (12 votes)
aaziz9014
Posted 8 years ago. Direct link to aaziz9014's post “at 1:05 what was that gre...”
at
1:05
what was that green thing
Button navigates to signup pageComment on aaziz9014's post “at 1:05 what was that gre...”
(7 votes)
Answer
- jbraddock
  Posted 7 years ago. Direct link to jbraddock's post “It is due to an incomplet...”
  It is due to an incomplete answer. Once you finish typing your answer, assuming it is an acceptable form for the particular question, the green guy goes away:)
  Button navigates to signup page
  (3 votes)
IJ
Posted 7 years ago. Direct link to IJ's post “Why he didn't multiply it...”
Why he didn't multiply it by 4 like:
100 - 4(3^2)pi? isn't this going to give us all four sides? o.O #confused

PS: Oh I get it, I get it now :D. (3^2)pi will give us the entire area of full circle :D
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(4 votes)
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Netert Johnson
Posted 5 years ago. Direct link to Netert Johnson's post “What if your book doesn't...”
What if your book doesn't give the area of the shape?
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(3 votes)
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eveymarie.cook
Posted a month ago. Direct link to eveymarie.cook's post “what is this website he's...”
what is this website he's using called?
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(3 votes)
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IsaLeen
Posted 2 months ago. Direct link to IsaLeen's post “it still doesn't make sen...”
it still doesn't make sence.
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(2 votes)
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Prisha
Posted 2 years ago. Direct link to Prisha's post “Why don't you multiply by...”
Why don't you multiply by four at the end instead of just 9π? Aren't you solving for four sides then subtracting?
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(3 votes)
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astevens4175
Posted 2 months ago. Direct link to astevens4175's post “Miss kindt I don’t get th...”
Miss kindt I don’t get this
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Ankush Sharma
Posted 7 years ago. Direct link to Ankush Sharma's post “find the area of shaded r...”
find the area of shaded region of square 6cm
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(3 votes)
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feli31
Posted 2 months ago. Direct link to feli31's post “_Why does it not have ans...”
Why does it not have answer?
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(2 votes)
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Video transcript

We're asked to find the area of the shaded region, so the area of this red-shaded region. So this is interesting. This is almost a 10 by 10 square, except we have these quarter circles that are cut out. So the area of this would be the area of what a 10 by 10 square would be minus the area of these quarter circles. And each of these quarter circles is a quarter of a circle with a radius 3. I think we can assume that all of these, if you took the distance from here to the outside of this quarter circle, have radius 3. So if you put four quarter circles together, you're going to have a complete white circle. So one way to think about this is that the area of this whole red region is going to be the area of the entire square, which is 10 by 10. So it's going to be 10 times 10, which is 100 whatever square units we have. And then we're going to subtract out the area of the four quarter circles. And that area is going to be equivalent to the area of one circle with a radius of 3. So what's the area of a circle with radius 3? Well, the formula for area of a circle is pi r squared, or r squared pi. So the radius is 3. So it's going to be 3 times 3, which is 9, times pi-- 9 pi. So we have 100 minus 9 pi is the area of the shaded region. And we got it right.