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Proving Trig identities

  1. May 15, 2010 #1
    1. How do I prove sinxcosxsec^2x=tanx



    2. Relevant equations
    sec^2x = tan^2x + 1


    3. The attempt at a solution


    sinxcosx(tan^2x + 1)
    tan^2xsinxcosx +sinxcosx
    sin^2x/cos^2x*sinxcosx + sinxcosx - is this valid?

    I'm not sure what I've done is even correct - but it doesn't seem to be going anywhere helpful?
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. May 15, 2010 #2
    Rewrite secant squared as 1/cos squared. The you'll have (sincos)/(coscos). Cancel cosines and you're done. I'll edit this from my computer and add arguments later!
     
  4. May 15, 2010 #3
    secant = 1/cosine
    cosecant = 1/sine
    cotangent = 1/tangent
     
  5. May 15, 2010 #4
    SOHCAHTOA. qed
     
  6. May 16, 2010 #5
    Many thanks for your help
     
  7. May 16, 2010 #6

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Wasn't that Lewis and Clark's indian guide?
     
  8. May 16, 2010 #7
    No, this is the one that's featured on the new US coins ;)
     
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