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Homework Help: Trigonometry equatation

  1. Nov 10, 2008 #1
    Sorry but i dont know how to use latex yet or to add mathematical symbols somehow.

    1. The problem statement, all variables and given/known data

    Prove that 1-sin2θ/cos2θ = 1-tanθ/1+tanθ

    2. Relevant equations

    sin2θ = 2tanθ/1+tan2θ and cos2θ =1-tan2θ/1+tan2θ

    I have allready proved from a previous exercise those two above so i pressume they may be useful.

    3. The attempt at a solution

    1-sin2θ/cos2θ = 1-2tanθ/1+tan2θ/1-tan2θ/1+tan2θ=

    i then multiply the fraction with (1+tan2θ) and i am left with


    i have tried various things but i suppose this is the way to go.. maybe not, i dont know, i am stuck. Can someone help me on that one please?
  2. jcsd
  3. Nov 10, 2008 #2
    Prove that (1-sin2θ)/cos2θ = (1-tanθ)/(1+tanθ)

    just replace the sine and cosine by the relevant equations that you cited.

    The exercise is quite straighforeward.

    you should come to (1-tanθ)^2/(1-tan^2(θ))

  4. Nov 10, 2008 #3
    Yes you told me exactly what i did :uhh:
    but for some reason i am stuck at this step. Its not that straight forward for me as it is for you :grumpy:
  5. Nov 10, 2008 #4

    Again i tell you : redo what you did because you calculated it incorrectly. What you give as your result is already incorrect ! Recalculate the substitutions

    ps : please, try to be polite to people that are trying to help you. Otherwise you won't last long here. Just a small piece of advice.
  6. Nov 10, 2008 #5
    Ok so my calculations were wrong i will try and work it out then, thanks.

    And btw i admire that you are helping people with their math problems but you did not help me with your first post, capitoo:)?
  7. Nov 10, 2008 #6
    If i didn't help you with my post then why do you say your calculations are wrong ?

    We are not gonna spoon feed the solution to you. That doesn't serve ANY purpose.
    I clearly stated what equation you should get if you did it properly and i also told you where your mistakes were made.

    Aside, giving you the solution, there is not much else to say

  8. Nov 10, 2008 #7
    You said that my calculations were wrong in your second post ... In your first post however you just said what i said, you sounded like a parrot.
  9. Nov 10, 2008 #8
    ok sorry i just read the post again you are right i am just a little dizzy to much math for me those days.... :)
  10. Nov 11, 2008 #9
    So, is the problem solved ?

  11. Nov 15, 2008 #10
    Yes problem solved o:)
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