Finding Circumference, given that radius is 12

[NightJay0044]

Hi, I'm new to these forums and it looks like a pretty good place for math knowledge.

Here is my question below....

"If a circle has a radius of 12', what is it's circumference most nearly?"

I get lost after looking at the first part of the question "The circle" I really dont know much at all about finding radiuses or circumferences..

What would I have to learn in order to answer this question more efficiently and also could someone answer it with an explanation?

Thanks..

 

[arthur ohlsten]

if radius is r
circumference is 2 pi r where pi=3.14159... irratioal number

circumference = 3.14159 times 12 answer
cir.=37.7' rounded to one decimal

 

[Mrspi]

In order to do these kinds of problems efficiently, you need to learn and commit to memory several formulas.

In a circle,

radius (which I'll denote as r) is the distance from the center of the circle to any point on the circle.

diameter (d) is the distance across the circle (passing through the center)
d = 2*r

circumference is the distance AROUND the circle
C = pi * diameter
or
C = 2 * pi * r

Area is the measure of the region INSIDE the circle.
A = pi * r<SUP>2</SUP>

pi is approximately 3.14159 (or to two decimal places, 3.14)

If you are given any one of these measures (r, d, C or A) you can use these formulas to find any of the others.