How do you find area when all you have is circumference (60cm)?

Divide by pi to get the diameter, then divide that by two to get the radius, then solve the formula for the area of a circle. pi r squared.

I understand pi x r squared, I understand how pi x r x r will get you the area, but the interactive illustration above shows area as 1/2 x circumference, and I'm not seeing that in the model. Can someone please explain?

It's not showing area as 1/2 * circumference. It is showing area = base * height. The base is 1/2 * circumference or πr. The height is r. So, area = πr².

what is the number of pi?

Here is a link to the first million digits: http://www.piday.org/million/

What is circumference relative to perimeter?

Perimeter = the distance around the outside (The definition my 3rd grade teacher gave) The circumference is the distance around the outside of a circle.

How would u work this problem

You divide the circumference of a circle by its diameter. If you want a more approximate value for this, go to http://www.piday.org/million/

Main content

NASA

Course: NASA > Unit 2

Lesson 3: Orbital mechanics

Applying pi

Google Classroom

Circumference

Using only this photo, could you find the circumference of this ferris wheel to within a few feet?

First we could take the height of a person who looks to be around 6 feet and figure out the radius of the circle:

5 * 6 = roughly 30 feet

With the radius we can use π to determine the circumference directly:

π = \frac{circumference}{diameter}

π = \frac{circumference}{2 \times r}

circumference = 2 \times π \times r

circumference \approx 2 \times 3.14 \times 30

circumference \approx 188 feet

We correctly find that it’s approximately 188 feet around the perimeter of the wheel, all thanks to π!

Area

How can we estimate the area of any circle given its radius?

Let’s approximate the answer using a pizza slice analogy. Below is an interactive illustration; click the arrows to change the number of slices in the pie:

As we increase n, the perimeter of the pizza approaches the circumference of the circle. As we increase the number of slices:

the height of the slice approaches the radius of the circle ( h = r )
the area of the pizza approaches the area of the circle ( area of pizza = area of circle )

This leads to a well-known equation which relates the area and radius of any circle:

area of circle = π r^{2}

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Andy K
Posted 8 years ago. Direct link to Andy K's post “How do you find area when...”
How do you find area when all you have is circumference (60cm)?
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- Lynn
  Posted 8 years ago. Direct link to Lynn's post “Divide by pi to get the d...”
  Divide by pi to get the diameter, then divide that by two to get the radius, then solve the formula for the area of a circle. pi r squared.
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tsavage
Posted 9 years ago. Direct link to tsavage's post “I understand pi x r squar...”
I understand pi x r squared, I understand how pi x r x r will get you the area, but the interactive illustration above shows area as 1/2 x circumference, and I'm not seeing that in the model. Can someone please explain?
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(3 votes)
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- Davin V Jones
  Posted 9 years ago. Direct link to Davin V Jones's post “It's not showing area as ...”
  It's not showing area as 1/2 * circumference. It is showing area = base * height. The base is 1/2 * circumference or πr. The height is r. So, area = πr².
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Jane Rudenko
Posted 9 years ago. Direct link to Jane Rudenko's post “Is there any other formul...”
Is there any other formulas for circle or ellipse?
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reallytriggered
Posted 9 years ago. Direct link to reallytriggered's post “what is the number of pi?”
what is the number of pi?
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- Squishy
  Posted 9 years ago. Direct link to Squishy's post “Here is a link to the fir...”
  Here is a link to the first million digits: http://www.piday.org/million/
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Michael Guilmette
Posted 10 years ago. Direct link to Michael Guilmette's post “What is circumference rel...”
What is circumference relative to perimeter?
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(1 vote)
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- Kendra
  Posted 9 years ago. Direct link to Kendra's post “Perimeter = the distance ...”
  Perimeter = the distance around the outside (The definition my 3rd grade teacher gave) The circumference is the distance around the outside of a circle.
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💥⭐️Khan academy🤑🍃 Metro
Posted 8 years ago. Direct link to 💥⭐️Khan academy🤑🍃 Metro's post “what does pi mean and how...”
what does pi mean and how did it get its simbol?
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Adrienne Camille Carter
Posted 9 years ago. Direct link to Adrienne Camille Carter's post “How would u work this pro...”
How would u work this problem
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- Shubhankar
  Posted 8 years ago. Direct link to Shubhankar's post “You divide the circumfere...”
  You divide the circumference of a circle by its diameter.
  If you want a more approximate value for this, go to http://www.piday.org/million/
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  (2 votes)
Josalyn
Posted 9 years ago. Direct link to Josalyn's post “sorry but this might be a...”
sorry but this might be a stupid question.....what does circumference mean? And how does pi=circumference/diameter help you find the circumference directly?
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💥⭐️Khan academy🤑🍃 Metro
Posted 8 years ago. Direct link to 💥⭐️Khan academy🤑🍃 Metro's post “What formula do you use t...”
What formula do you use to work this out?
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Saagar CD
Posted 8 years ago. Direct link to Saagar CD's post “how do we find out the re...”
how do we find out the relation Circumference=2*pi*r
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