How do you find the length of an arc?

Question

anonymous · Answer

If you know the angle of the arc, it's simply:
x/360*2pi*r

hero · Answer

$$\frac{\theta}{360^{\circ}} = \frac{x}{2 \pi r}$$ x = arc length

anonymous · Answer

Length of arc S = r * θ
r radius and θ is central angle

hero · Answer

chlorophyll, you forgot to add that θ must be in radians before calculating arc S

anonymous · Answer

Oops, what 's huge mistake! 
Thanks for reminding me, Hero! ( Knock myself on the head :P)

hero · Answer

I just think that only one formula should be used. I prefer mine because it's in the form of a proportion which to me is much easier to remember because of the "part-whole" relationship. I learned this ratio a while back

$$\frac{\theta}{360} = \frac{x}{2 \pi r} = \frac{y}{\pi r^2}$$ where :
θ = angle in degrees
x = arc length
y = area of sector

anonymous · Answer

What a great relation of angle, circumfence and area! (taking note right now!) Thank you so much, Hero!

hero · Answer

Don't thank me, thank Debra Anne Ross. She wrote the Master Math series for Basic Math thru Calculus. Well, someone I know at the University I attended wrote the Master Math portion for probability, but it's not that good of a book unfortunately. But Debra Anne Ross's explanations are perfect.