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

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- Sep 23rd 2008, 12:25 PMLouismoore16Circumference 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 PMicemanfan
The formula for circumference C of a circle with diameter d is $\displaystyle C = \pi{d}$.

- Sep 23rd 2008, 12:33 PMLouismoore16
could you explain more please

so it would be ...c= pie x 12.3

??

- Sep 23rd 2008, 12:35 PMicemanfan
- Sep 23rd 2008, 12:44 PMLouismoore16
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 PMicemanfan
Your answer is correct.

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 PMmasters
- Sep 23rd 2008, 01:11 PMLouismoore16
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 PMicemanfan
Looks good to me, again assuming that you are rounding to the nearest tenth.