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: 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



    tan(2x)*(tan(x))^2=-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

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    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
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook