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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


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    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))?
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