Question

Find the exact circumference of a circle with an area equal to 36 sq. in.

a. 12 pi
b. 18 pi
c. 324 pi

Answer 1

12 Pi

Answer 2

How do you find the radius from this info? Or lack thereof

Answer 3

A = pi*r^2

36 = 3.14*r^2

solve for r to get r = ???

once you know the value of r, you can find the circumference C

C = 2*pi*r

Answer 4

But how do you find R? Thats where Im stuck

Answer 5

the question wants the circumference function in pi... so we can get the relation

Answer 6

did you divide both sides of 36 = 3.14*r^2 by 3.14 ?

Answer 7

No.

Answer 8

what do you get when you do so

Answer 9

Well 36/3.14 is 11.46

Answer 10

now if r^2 = 11.46, then what must r be?

Answer 11

What does ^ mean?

Answer 12

r^2 means r squared

Answer 13

r^2 = r*r

Answer 14

for example, 5^2 = 5*5 = 25

Answer 15

So multiply 11.46 by 11.46?

Answer 16

Wait, no. 5.73 multiplies by 5.73?

Answer 17

Multiplied?

Answer 18

some number, multiplied by itself, gives 11.46

Answer 19

to find this number, you take the square root of 11.46

Answer 20

it turns out that

sqrt(11.46) = 3.385 roughly

which means 3.385*3.385 = 11.458225, pretty close to 11.46

Answer 21

So then i have 36=3.14*3.38^2?

Answer 22

now use that r value to find the circumference C

use C = 2*pi*r

Answer 23

So two times pi times 3.38?

Answer 24

2 times pi times 3.38

Answer 25

oh sry didn't see your two, nvm

Answer 26

yes you are correct

Answer 27

21.23 is what I got.

Answer 28

Question: does the original "36" given in the problem also have a "pi" attached to it?

Answer 29

Yes

Answer 30

ok so that changes things a bit

Answer 31

Sorry.

Answer 32

if the area is A = 36pi, then

A = pi*r^2
36pi = pi*r^2
36 = r^2 ... the pi terms cancel

if r^2 = 36, then r = ??

Answer 33

6?

Answer 34

yes, then you plug that into C = 2*pi*r

Answer 35

37.69?

Answer 36

notice how each answer has a 'pi' in it

so ignore the pi for now

compute 2*r and then tack on 'pi' at the end

Answer 37

example: if r = 7, then 2*pi*r = 14pi

Answer 38

Im still getting the same thing.

Answer 39

you should get 12pi

Answer 40

2 times R which is 6 means 12.
Then 12*pi. The answer I'm getting is still 37.69

Answer 41

2*r = 2*6 = 12

Answer 42

you leave it as 12pi

Answer 43

OH! Okay.

Answer 44

Thank you so much! Sorry I am so bad at this!

Answer 45

whenever you see the key term "exact" that means to leave the 'pi's as they are

Answer 46

you did good

Answer 47

Oh. Sounds good.
Thank you that means a lot!

Answer 48

you're welcome