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Trigonometric equation

  1. Dec 27, 2009 #1
    1. The problem statement, all variables and given/known data
    The original problem is this: ab^2*cos(2x)*(cos(x))^2 + ba^2*sin(2x)*(sin(x))^2 = 0
    And some of the more "logical" forms I've got to are these:

    2[tan(x)]^3-2tan(x) = -b/a


    But I can't solve these equations so I'd like to ask for some help here.
    Last edited: Dec 27, 2009
  2. jcsd
  3. Dec 27, 2009 #2


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    Hi kristo! :smile:

    (try using the X2 tag just above the Reply box :wink:)
    That's the one!

    Now just write tan(2x) in terms of tanx, and solve. :wink:

    (eugh … it's a cubic :yuck:)
  4. Dec 30, 2009 #3
    try to assign a variable like u to tanx
    then establish a relation between tanx and tan2x
    and then write both equations in terms of u and equate both to each other
    and then solve the resultant equation for u
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