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!

Homework Help: Trigonometric limit problem

  1. Sep 4, 2011 #1
    1. The problem statement, all variables and given/known data

    Find [itex]\lim_{x \to 0}\frac{1-cosxcos2xcos3x}{1-cosx}[/itex]

    3. The attempt at a solution

    Actually my book gives this continuation [itex]\lim_{x \to 0}\frac{1-cosx+cosx[1-cos2x+cos2x(1-cos3x)]}{1-cosx}[/itex] but I don't know how author arrived there. Can anyone explain it to me?

    Thank you
    Last edited: Sep 4, 2011
  2. jcsd
  3. Sep 4, 2011 #2
    The author rewrote the numerator; if you expand all brackets, you arrive at the same expression.
  4. Sep 4, 2011 #3
    Yeah, I realized, after I posted this thread, that author added and substracted [itex]cosx[/itex] in numerator. This was the trick.

    The problem is solved.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook