Results 1 to 4 of 4

Math Help - [SOLVED] Having trouble with this identity

  1. #1
    Newbie
    Joined
    Feb 2010
    Posts
    6

    [SOLVED] Having trouble with this identity

    I've been at this for a little while now but I'm not quite sure how to proceed. Would someone please help me?

    Cos3(theta) = 4Cos^3(theta) - 3Cos(theta)
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Newbie
    Joined
    Feb 2010
    Posts
    6
    Also I'm only supposed to manipulate a single side of the equation.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    11,621
    Thanks
    426
    Quote Originally Posted by Lucian View Post
    I've been at this for a little while now but I'm not quite sure how to proceed. Would someone please help me?

    Cos3(theta) = 4Cos^3(theta) - 3Cos(theta)
    \cos(3t) =<br />

    \cos(2t+t) =

    \cos(2t)\cos(t) - \sin(2t)\sin(t) =

    [2\cos^2(t) - 1]\cos(t) - 2\sin^2(t)\cos(t) =

    [2\cos^2(t) - 1]\cos(t) - 2[1 - \cos^2(t)]\cos(t) =


    finish it ...
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Feb 2010
    Posts
    6
    I think I've got it, thank you for the help Skeeter!

    (2Cos^3(t)-Cos(t)) - (2)(Cos(t)-Cos^3(t))
    (2Cos^3(t)-Cos(t)) - (2Cos(t) - 2Cos^3(t))
    2Cos^3(t) -Cos(t) - 2Cos(t) + 2Cos^3(t)
    4Cos^3(t) - 3Cos(t)
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 5
    Last Post: July 14th 2009, 10:24 PM
  2. Replies: 1
    Last Post: February 11th 2009, 12:35 PM
  3. more trouble completing identity...
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: November 5th 2008, 04:14 AM
  4. [SOLVED] Multiple regression equation trouble
    Posted in the Advanced Statistics Forum
    Replies: 1
    Last Post: August 2nd 2007, 01:10 PM
  5. [SOLVED] Gradient trouble! Oh oh
    Posted in the Math Topics Forum
    Replies: 1
    Last Post: January 26th 2006, 02:28 PM

Search Tags


/mathhelpforum @mathhelpforum