# Circumference help!

• Sep 23rd 2008, 12:25 PM
Louismoore16
Circumference help!
Hey, just a quick question
do you know how to find the circumference of a circle by using the diameter
do if the diameter is 12.3cm what would it be and how would you work it out ?
thanks
• Sep 23rd 2008, 12:27 PM
icemanfan
The formula for circumference C of a circle with diameter d is $\displaystyle C = \pi{d}$.
• Sep 23rd 2008, 12:33 PM
Louismoore16
so it would be ...c= pie x 12.3
??
• Sep 23rd 2008, 12:35 PM
icemanfan
Quote:

Originally Posted by Louismoore16
so it would be ...c= pie x 12.3
??

Yes, that is correct.
• Sep 23rd 2008, 12:44 PM
Louismoore16
right so would the answer for c=piex12.3= 38.6

and how do i work out the area of a circle using the diameter??
• Sep 23rd 2008, 01:03 PM
icemanfan

The area A of a circle with radius r is $\displaystyle A = \pi{r^2}$. Since r is half of d, the formula could be written as $\displaystyle A = \pi{(0.5d)^2} = 0.25\pi{d^2}$.
• Sep 23rd 2008, 01:06 PM
masters
Quote:

Originally Posted by Louismoore16
right so would the answer for c=piex12.3= 38.6

and how do i work out the area of a circle using the diameter??

That would be correct to the nearest tenth. And, it's "pi" not "pie".

I like pie. But, did you know that in Alaska, pi has only a value of 3. I suppose the cold shrinks everything. They call it "Exkimo Pi". Just kidding!(Evilgrin)
• Sep 23rd 2008, 01:11 PM
Louismoore16
right so just let me check to see if this is right, if it is im sorted
the question was find the area of a circle using diameter=14.8cm
so i do 14.8 divided by 2=7.4 then pie x 7.4squared=172.3
is this right?
• Sep 23rd 2008, 01:14 PM
icemanfan
Looks good to me, again assuming that you are rounding to the nearest tenth.