• Dec 2nd 2008, 11:47 PM
mathmom
This seems really basic to everything else I see posted... hopefully I can get some help.. asap Thank you!

A circular window has an area of 10 square feet. Find the circumference of the window.
• Dec 2nd 2008, 11:51 PM
Chop Suey
The area of a circle is given by:
$A = \pi r^2$

The circumference of a circle is given by:
$C = 2\pi r$

Find the radius from the given area, then find the circumference.
• Dec 3rd 2008, 12:16 AM
mathmom
thank you.. I guess I need a little more help, cause I have that info, I am not sure how to do that part though.

I have the area at 10 ft ^2
so how do I figure the circumference with that? I guess first figure out the radius? and how do I do that?

thank you so much! really.. sorry for needing more help... hope you can help me!
• Dec 3rd 2008, 12:33 AM
mr fantastic
Quote:

Originally Posted by mathmom
thank you.. I guess I need a little more help, cause I have that info, I am not sure how to do that part though.

I have the area at 10 ft ^2
so how do I figure the circumference with that? I guess first figure out the radius? and how do I do that?

thank you so much! really.. sorry for needing more help... hope you can help me!

Solve $10 = \pi r^2$ for r: $r^2 = \frac{10}{\pi} \Rightarrow r = \, ....$

Then substitute the value for r into $C = 2 \pi r$.
• Dec 3rd 2008, 06:49 AM
mathmom
Thank you.. could you check this and see if it is correct?
r^2=10/pi
3.183098862=r^2

20=2(pi)(3.183098862)
so the cirucumference is 20? is that right?
• Dec 3rd 2008, 07:30 AM
Chop Suey
You substituted $r^2$ instead of $r$, which is wrong.

$r^2 = \frac{10}{\pi}$

$r = \sqrt{\frac{10}{\pi}} \approx 1.78412411615$