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-   -   How do you prove this identity? (https://www.askmehelpdesk.com/showthread.php?t=543081)

  • Jan 11, 2011, 06:00 PM
    ellenegaudet
    How do you prove this identity?
    (tan^4x)-(tan^2x)(sec^2x) = -tan^2x
  • Jan 11, 2011, 10:07 PM
    Unknown008

    You can do it in a very simple way starting by factoring tan^2x.





    Then, recall the pythagoras' identify:



    Divide this by cos^2x to give:



    This means that

    Substitute that in



    What do you get? :)

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