1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Trig identities, prove (cot(x)-tan(x)=2tan(2x))

  1. May 6, 2014 #1
    1. The problem statement, all variables and given/known data
    Prove cot(x) - tan(x) = 2tan(2x)


    2. Relevant equations
    Trig identities
    http://en.wikipedia.org/wiki/List_of_trigonometric_identities

    3. The attempt at a solution
    I have worked it down and don't think they are equal. I think it's supposed to be 2cot(2x) not 2tan(2x), that is what I found. Am I correct or what have I done wrong?
    Thanks
     

    Attached Files:

  2. jcsd
  3. May 6, 2014 #2

    CAF123

    User Avatar
    Gold Member

    Yes, I get the same result as you, although your calculation was a lot more complicated. If you let x=π/4, the LHS is zero while the RHS is undefined. So it cannot be 2tan(2x) for the equation to be an identity.
     
  4. May 6, 2014 #3
    Thanks for the fast reply, my teacher wanted full working with identities so that's why it's in long form. I am not sure if it is a mistake or if it is a trick question, thanks.
     
  5. May 6, 2014 #4

    CAF123

    User Avatar
    Gold Member

    Most likely a mistake unless the question wanted you to find what particular subset of x satisfies the equation. But if it says 'Prove..' then that is not the case.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Trig identities, prove (cot(x)-tan(x)=2tan(2x))
  1. Prove trig identities (Replies: 1)

  2. Prove trig identity (Replies: 10)

Loading...