anonymous
  • anonymous
HELP WILL MEDAL AND FAN! Find the area of the circle: Inner radius is 4cm, Outer radius is 9cm.
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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chestercat
  • chestercat
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anonymous
  • anonymous
Here are the options. A) 78.5cm^2 B) 31.4cm^2 C) 157cm^2 D) 204.1cm^2
ganeshie8
  • ganeshie8
are you trying to find the area of region between below two circles ? |dw:1440600185673:dw|
Astrophysics
  • Astrophysics
Note the area for a circle is \[A_{circle} = \pi r^2\]

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anonymous
  • 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
  • Astrophysics
|dw:1440600531344:dw| so like this
anonymous
  • anonymous
Yes except colored all the way in the ring part.
ganeshie8
  • ganeshie8
|dw:1440600652512:dw|
Astrophysics
  • Astrophysics
Show off!
ganeshie8
  • ganeshie8
definitely! ;)
anonymous
  • anonymous
Yes the bottom one looks like it.
ganeshie8
  • ganeshie8
there is a little trick to get that black area
ganeshie8
  • ganeshie8
do u remember how to find area of full circle ?
anonymous
  • anonymous
Nope.
ganeshie8
  • ganeshie8
you will need to know that before attempting this problem
ganeshie8
  • ganeshie8
lets do a quick problem maybe
anonymous
  • anonymous
K
ganeshie8
  • ganeshie8
Find area of region interior to below circle of radius 3 units : |dw:1440600874779:dw|
anonymous
  • anonymous
How do I set this up?
ganeshie8
  • ganeshie8
there is a direct formula look up in ur notes/google for "area of circle"
Astrophysics
  • Astrophysics
Also you can scroll up, I mentioned it above :P
anonymous
  • 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
  • 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
  • anonymous
So I would multiply 4cm and 9cm by 3.14r1 and 3.14r2?
Astrophysics
  • Astrophysics
r is the radius
anonymous
  • anonymous
I know, so what do I do first.
Astrophysics
  • Astrophysics
You just have to plug it into the formula \[A = (4)^2\pi\]
Astrophysics
  • Astrophysics
And do the same for the r = 9 then subtract it from your area with r = 4
anonymous
  • 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
  • Astrophysics
Use 3.14 unless your question states otherwise there are also many calculators online you can use, http://www.wolframalpha.com/
anonymous
  • anonymous
Thank you I figured it out!
Astrophysics
  • Astrophysics
Yw

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