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Triginometry - very annoying

  1. May 1, 2005 #1
    The first part of this question was to find the roots of the equation 2x^3-5x^2-4x+3=0 i got x=-1, 3, and 1.

    but then the second part completely confused me
    b) Hence, by substituting x=cost solve the equation 2cos^3t-5cos^2t -4cost+3=0 for 0<t<2"pie", giving your answer in radians in terms of pie.

    PLEASE HELP! :confused: :confused: :confused: :grumpy:
  2. jcsd
  3. May 1, 2005 #2


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    Can you solve cos(t)=-1?

    Oh, you've solve the cubic equation wrong, 1 of the solutions for x does not work.
    Last edited: May 1, 2005
  4. May 1, 2005 #3
    The roots are : x=-1,3,1/2.

    Just solve : cos(t)=-1 and cos(t)=1/2...this gives of course an infinity of real answers...

    If you allow complex numbers, then you can solve cos(t)=3...

    NB : You're great, with your help I know how the english pronounciation of [tex]\pi[/tex] double explain it's origin :biggrin:
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