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Homework Help: Factor Formulae

  1. Jun 24, 2011 #1
    Hi all,

    I have an exam today but the questions which will come up I have never come across before. Some of the questions involve the Factor Formulae which I have never seen before so I was wondering whether you might give some examples and perhaps links to other pages where I can take a long revision.

    1. Using the factor formulae evaluate the integrals of the type (sinx cos3x)dx

    2. Use the factor formulae to prove trig identities.

    I have a general understanding of Trigonometry and I have just completed my Calculus.

    We've just been told today about this exam and I have no idea how the factor formulae looks like and how to use it.


    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution

    For prove trig using the Factor formulae:

    Prove that: 4(cosx + cos2x)sin3xsinx = cos4x - cos8x

    My take:

    =2(cosx + cos2x) 2sin3xsinx
    Reverse using factor formulae
    =2(cosx + cos2x)(cos4x - cos2x)
  2. jcsd
  3. Jun 24, 2011 #2


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    Science Advisor
    Homework Helper

    Hi Googl! :smile:
    nooo, wrong direction :redface:

    general rule of thumb: always try to make things simpler, not more complicated! :biggrin:

    sinsin is simpler than (cos + cos), so use the factor formula https://www.physicsforums.com/library.php?do=view_item&itemid=18" on everything except the sin3xsinx :wink:
    Last edited by a moderator: Apr 26, 2017
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