Results 1 to 2 of 2

Math Help - Identities help...

  1. #1
    Junior Member
    Joined
    Jan 2008
    Posts
    53

    Identities help...

    I'm stuck on this question:

    Prove identity: 1-tanѲsin2Ѳ=cos2Ѳ

    I understand i have to use this formula sin 2A=2sinAcosA but i don't know what to do from there..
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor red_dog's Avatar
    Joined
    Jun 2007
    From
    Medgidia, Romania
    Posts
    1,245
    Thanks
    1
    We have \cos\theta=\cos^2\theta-\sin^2\theta=2\cos^2\theta-1=1-2\sin^2\theta

    Now, 1-\tan\theta\sin 2\theta=1-\frac{\sin\theta}{\cos\theta}\cdot 2\sin\theta\cos\theta=1-2\sin^2\theta=\cos 2\theta
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 6
    Last Post: June 22nd 2010, 11:59 PM
  2. Identities
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: March 9th 2010, 04:13 PM
  3. Identities
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: March 7th 2010, 10:19 PM
  4. Identities
    Posted in the Trigonometry Forum
    Replies: 4
    Last Post: March 7th 2010, 05:39 PM
  5. set identities
    Posted in the Discrete Math Forum
    Replies: 5
    Last Post: April 12th 2009, 02:57 PM

Search Tags


/mathhelpforum @mathhelpforum