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Homework Help: Trig Identity stumped

  1. Nov 27, 2008 #1
    1. The problem statement, all variables and given/known data

    Show that the LHS can be changed into the RHS.
    [tex] sec^6 x-tan^6x=1+3sec^2x tan^2x[/tex]

    2. Relevant equations

    Trig identities.

    3. The attempt at a solution
    I tried factoring the LHS:
    [tex]sec^2-tan^2=1[/tex] so that leaves me with the other thing in the parentheses. I have tried using the Pythagorean identities on sec^2 and tan^2, I have broken up the sec^4 into sec^2*sec^2.....

    I just am not getting anywhere.
    Pointers would be nice.
  2. jcsd
  3. Nov 27, 2008 #2
    i get the RHS le.
    try (tan²x+1)³ - tan^6 x
    then you expand.

    i will be offline , i shall leave the ans in the spoiler (:

    next step:
    3tan²x+3tan^4 x +1
    Last edited: Nov 27, 2008
  4. Nov 29, 2008 #3
    I got it easily after the first hint. Thanks! I had been staring at it too long to see another way.
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