1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Help with a limit.

  1. Dec 18, 2011 #1
    1. The problem statement, all variables and given/known data

    question asks:

    lim(x,y) -> (0,0)

    cos(xy) -1 / [x^2 y^2]

    2. Relevant equations

    3. The attempt at a solution

    if you multiply the top and bottom by cos(xy) + 1 you get

    -[sin^2(xy)/(xy)^2] * [1/cos(xy) + 1]

    but in the solution they somehow got rid of the denominator (xy)^2, because if that's there the denominator is still 0. How do you get rid of that?
  2. jcsd
  3. Dec 18, 2011 #2


    User Avatar
    Science Advisor
    Homework Helper

    The limit u->0 sin(u)/u=1. So limit u->0 sin(u)^2/u^2=1. That's what they did with the first term.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Help with a limit.
  1. Limit help (Replies: 5)

  2. Help with Limits (Replies: 5)

  3. Help with limits (Replies: 4)

  4. Help with a limit (Replies: 3)

  5. Limit help (Replies: 3)