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## nynic819 2 years ago The circumference of a circle is 31.4 feet. What is the area of the circle? Explain how you found your answer.

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1. dave0616

First off you will need to know the formula for the area of a circle, which is A=pi*radius*radius. next you will need to know the formula for the circumfrence of a circle, which is 2*pi*r=Circ. You know that circumfrance is equal to 31.4 feet, so set that equal to the equation for circumfrence to find r. \[31.4 ft = 2*3.14*r\] because pi is equal to 3.14. Multiply 3.14 by 2 to get 6.28. 31.4 ft = 6.28*r divide 31.4 by 6.28 and you will get r. 5 ft = r. you will then take that information and put it into the equation to find the area: A=pi*r*r A=pi*5*5 can you figure out Area from there?

2. nynic819

no..I do not understand. Sorry

3. dave0616

thats fine, the only i can help you more is if you tell me if you dont understand. Ok so you are looking for area, and the formula for the area of a circle is always: Area= pi*radius*radius. but you are given circumfrance. do you have it up until there?

4. nynic819

yes

5. dave0616

ok, you are given the circumference of the circle, at 31.4 feet. The formula for the circumference of a circle is always C=2*pi*r. and you are given circumference, so set the equation to the value given to give you the formula: 31.4 feet = 2* pi * radius. Are we clear up until here?

6. nynic819

yes

7. dave0616

ok, so we need to solve for radius because that is what we need for the equation of area. both 2 and pi are constants, so we can multiply pi by 2, and divide 31.4 feet by the product of 2 and pi, so the work will look like this: 31.4 feet = 2*pi*radius 31.4 feet = 6.28* radius (6.28 because has an accepted working value at 3.14) now divide 31.4 by 6.28 5= radius. Clear up until this point?

8. nynic819

yes :)

9. dave0616

ok, so you now know that the formula for area is A=pi*radius*radius. Solve for area now that you solved for radius. Can you figure this out?

10. nynic819

pi *5*5 = 3.14 x 5 x 5 = 81 ?

11. dave0616

not quite, you have the equation set up right, i would just punch that back into a calculator, because i am getting a number that is close to that, but not exactly

12. nynic819

Not using a calculator...lol

13. nynic819

78.5 my mistake...lol

14. nynic819

So that is my answer? 78.5?

15. dave0616

yes, the answer is 78.5

16. nynic819

and if I needed the diameter I would divide in half?

17. dave0616

nope, diameter is two times the radius. so you would multiply by 2

18. dave0616

but the formulas do not use diameter, so if you are given diameter, you must divide diameter by 2 to get the radius. dont use diameter when you have to use radius

19. nynic819

ok. Thanks. That's helped alot. Have to go to bed now. Big test tomorrow. Wish me luck :) Have a great night :)

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