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: How did this transition occur?

  1. Oct 5, 2012 #1
    lim as x-> 0 (2-cos3x-cos4x)/(x).

    I'm not sure how the numerator became (1-cos3x)(1-cos4x)/(x)

    What am I missing? Could someone please point it out? Is it a trignometric factoring formula I'm not thinking of?
     
  2. jcsd
  3. Oct 5, 2012 #2

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    It's difficult to answer this without you providing more context, but here's a try.

    (2-cos(3x)-cos(4x)) ≠ (1-cos(3x))(1-cos(4x)).

    However, (2-cos(3x)-cos(4x)) = (1-cos(3x)) + (1-cos(4x)) .
     
  4. Oct 5, 2012 #3
    So how did the numerator become: (2-cos(3x)-cos(4x)) = (1-cos(3x)) + (1-cos(4x))?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook