# Math Help - Circumference help!

1. ## 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

2. The formula for circumference C of a circle with diameter d is $C = \pi{d}$.

3. could you explain more please
so it would be ...c= pie x 12.3
??

4. Originally Posted by Louismoore16
so it would be ...c= pie x 12.3
??
Yes, that is correct.

5. 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??

The area A of a circle with radius r is $A = \pi{r^2}$. Since r is half of d, the formula could be written as $A = \pi{(0.5d)^2} = 0.25\pi{d^2}$.

7. 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!

8. 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?

9. Looks good to me, again assuming that you are rounding to the nearest tenth.