Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

B Circumference of a circle

  1. Sep 15, 2016 #1
    I just have a little question that i have read in the book of Thomas/Finney Calculus 9th edition that the circumference of a circle is 2pi,i can be wrong obviously but wasn't it supposed to be 2*pi*radius of the circle?
    Please help.
     
  2. jcsd
  3. Sep 15, 2016 #2

    berkeman

    User Avatar

    Staff: Mentor

    Both are correct if the radius r = 1. Can you scan the page in question and UPLOAD it?
     
  4. Sep 15, 2016 #3

    Math_QED

    User Avatar
    Homework Helper

    Most likely, they calculated the length of the curve ##y = \sqrt{1 - x^2}##. This is the unit circle with radius ##1## and thus the circumference is equal to ##2\pi##.

    If they would have calculated the length of the curve ##y = \sqrt{r^2 - x^2}##, the circumference would be equal to ##2\pi r##. This is the circle through the origin with radius ##r##.
     
  5. Sep 15, 2016 #4
    Oh, yes, thank you, they have said about the unit circle at first then said that it's circumference is 2pi. Sorry,I didn't notice . But thank you again, I was really confused.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted