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Simplify with Trigonometric Identities

  1. Sep 6, 2014 #1
    1. The problem statement, all variables and given/known data

    I'm trying to simplify some trigonometric expressions, I'm attaching my work here. This comes from a famous physics problem i.e. the rod with two masses spinning on a circle. I've tried many times but I just can't get it. Any help on which identities to use would really help me.

    2. Relevant equations

    I'm attaching the simplified version, the 'answer'

    3. The attempt at a solution

    I'm attaching my work.

    Attached Files:

  2. jcsd
  3. Sep 6, 2014 #2


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    Staff: Mentor

    Apply a couple of times sin2 x + cos2 x = 1
    and your last line simplifies to the given answer
  4. Sep 6, 2014 #3
    Yes, I looked at that identity, but there are 2 different angles in this problem, and also one of my last two terms is dø2*sin2Θ

    Any direction on how to first apply the identity would also help?
  5. Sep 6, 2014 #4


    User Avatar

    Staff: Mentor

    Take cos2 θ outside some brackets because it's a common factor.

    And you'll see again, there's another common factor in two other terms to treat similarly.
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