Results 1 to 5 of 5

Math Help - Proving Identity #2

  1. #1
    Senior Member
    Joined
    Nov 2008
    Posts
    425

    Proving Identity #2

    Prove
    cot(theta)-tan(theta)=2cot(theta)

    LS:

    So far I have

    cos(theta)/sin(theta)-sin(theta)/cos(theta)
    =[cos^2(theta)-sin^2(theta)]/sin(theta)cos(theta)
    =cos2(theta)/sin(theta)cos(theta)

    I am stuck as to where to go now.
    Can someone help me please?
    Last edited by mr fantastic; August 12th 2009 at 04:25 PM. Reason: Changed post title
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    11,628
    Thanks
    430
    Quote Originally Posted by skeske1234 View Post
    Prove
    cot(theta)-tan(theta)=2cot(theta)
    as posted, the above is not an identity.

    perhaps you meant ...

    \cot{\theta} - \tan{\theta} = 2\cot(2\theta)

    ???
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Senior Member
    Joined
    Nov 2008
    Posts
    425
    Quote Originally Posted by skeeter View Post
    as posted, the above is not an identity.

    perhaps you meant ...

    \cot{\theta} - \tan{\theta} = 2\cot(2\theta)

    ???

    no no, the question says:
    cot(theta)-tan(theta)=2cot(theta)

    Ok, so if it is not an identity, how do I prove or know that it is not one?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    11,628
    Thanks
    430
    Quote Originally Posted by skeske1234 View Post
    no no, the question says:
    cot(theta)-tan(theta)=2cot(theta)

    Ok, so if it is not an identity, how do I prove or know that it is not one?
    show the equation is false for at least one value of \theta ... try \theta = \frac{\pi}{4}, see what happens.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Apr 2009
    Posts
    44
    Quote Originally Posted by skeske1234 View Post
    no no, the question says:
    cot(theta)-tan(theta)=2cot(theta)

    Ok, so if it is not an identity, how do I prove or know that it is not one?
    yeah skeske1234 is correct
    If so
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Proving an identity
    Posted in the Trigonometry Forum
    Replies: 5
    Last Post: July 17th 2011, 12:23 PM
  2. Proving Another Identity
    Posted in the Trigonometry Forum
    Replies: 7
    Last Post: June 6th 2011, 10:34 AM
  3. Help proving an identity
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: April 22nd 2010, 11:57 AM
  4. Proving an identity that's proving to be complex
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: July 21st 2009, 01:30 PM
  5. proving an identity
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: March 16th 2008, 10:03 AM

Search Tags


/mathhelpforum @mathhelpforum