Replies

1. 
   ChuckN | Jan 20, 2007 03:01am | #1

   it's been a while but...radius x pi (3.14)?

    

    

   I spent a fortune on deodorant until I finally realized that people didn't like me anyway.

2. 
   jeanlou | Jan 20, 2007 04:15am | #2

   Hi Tom,

   I can not do it using a single formula, but I can do it as follows:

   Divide the length of the chord by the radius. This will give you a value that you can look up in a table of trigonometric functions that is the tangent of the angle formed by joining the two extremities of the chord to the center of the circle. Using this tangent value you can look up the angle it is associated with.

   To find the arc length, multiply the (angle) by (pi (3.141592) divided by 180). Then multiply the result by the radius.

   If you have a scientific calculator, then you will not need the tables. I believe that the windows XP calculator has a scientific function.  JL

   
   

   ---

   Edited 1/19/2007 8:18 pm ET by jeanlou

3. 
   gorilla1 | Jan 20, 2007 02:58pm | #3

   I've been doing some arcs in my table work. Check out the following link:
   http://www.1728.com/indexgeo.htm

   Goof luck

   Burt

4. 
   shopteacher | Jan 20, 2007 03:11pm | #4

   Wow! A formula you say.  Here's and example, is this what you are looking for and if so I'm going to keep looking for the formula?

   
5. 
   Jfrostjr | Jan 20, 2007 05:07pm | #5

   Here is the formula:

   Arc = 0.017453rA

   where "r" = radius;

   and "A" = the included angle of the arc;

   Frosty

6. 
   Jfrostjr | Jan 20, 2007 05:12pm | #6

   Sorry. I misread your question. Try this one:

   Chord "c" = 2 x r x sin A/2

   Frosty

1. 
   TomHigby | Jan 21, 2007 01:27am | #7

   The length of the chord is given. It's the length of the arc that is sought.

   Thanks for the reply.

   Tom

1. 
   [email protected] | Jan 21, 2007 01:51am | #8

   Tom, use Frosty's formula to get the angle, then it is:

   Pi X D X (Angle/360)

7. 
   dstevick | Jan 21, 2007 02:11am | #9

   To find the arc length when given the radius and cord length use the following formula:

   Arclength = 2 * radius * arcsin( cord / (2 * radius ) )

   This only works if your calculator is set to use radians vs. degrees for trig functions. If not multiply the value by ( 2 * π / 180 ) or 0.03491

   Good Luck,

   Dean

8. 
   TomHigby | Jan 21, 2007 06:53pm | #10

   Friends, my thanks to the many responders.  My college trig course was fifty years ago, and somewhat rusty.

   Tom