HELP WILL MEDAL AND FAN!
Find the area of the circle: Inner radius is 4cm, Outer radius is 9cm.

- anonymous

HELP WILL MEDAL AND FAN!
Find the area of the circle: Inner radius is 4cm, Outer radius is 9cm.

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- anonymous

Here are the options.
A) 78.5cm^2
B) 31.4cm^2
C) 157cm^2
D) 204.1cm^2

- ganeshie8

are you trying to find the area of region between below two circles ?
|dw:1440600185673:dw|

- Astrophysics

Note the area for a circle is \[A_{circle} = \pi r^2\]

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## More answers

- anonymous

The diagram I was given asked me to figure out the area of the shaded region of the circle it showed me. The entire ring of the circle was faded in, but the middle part with the hole was not. To answer your queston yes I think.

- Astrophysics

|dw:1440600531344:dw| so like this

- anonymous

Yes except colored all the way in the ring part.

- ganeshie8

|dw:1440600652512:dw|

- Astrophysics

Show off!

- ganeshie8

definitely! ;)

- anonymous

Yes the bottom one looks like it.

- ganeshie8

there is a little trick to get that black area

- ganeshie8

do u remember how to find area of full circle ?

- anonymous

Nope.

- ganeshie8

you will need to know that before attempting this problem

- ganeshie8

lets do a quick problem maybe

- anonymous

K

- ganeshie8

Find area of region interior to below circle of radius 3 units :
|dw:1440600874779:dw|

- anonymous

How do I set this up?

- ganeshie8

there is a direct formula
look up in ur notes/google for "area of circle"

- Astrophysics

Also you can scroll up, I mentioned it above :P

- anonymous

I did some reading about it from a Google search which took me to a website called "Math Goodies", and after reading it still don't understand it any better then before.

- Astrophysics

Well the area of a circle is \[A=\pi r^2\] I guess if you want to know more about it watch this video https://www.khanacademy.org/math/geometry/basic-geometry/circum_area_circles/v/circles-radius-diameter-and-circumference
And for your question the Shaded area = area of outer shape – area of inner shape

- anonymous

So I would multiply 4cm and 9cm by 3.14r1 and 3.14r2?

- Astrophysics

r is the radius

- anonymous

I know, so what do I do first.

- Astrophysics

You just have to plug it into the formula \[A = (4)^2\pi\]

- Astrophysics

And do the same for the r = 9 then subtract it from your area with r = 4

- anonymous

How would I enter pi into the computer? The calculator I'm using is on the computer, and it does not have a pi symbol.

- Astrophysics