Results 1 to 2 of 2

Math Help - Trig identities.

  1. #1
    Newbie
    Joined
    Dec 2007
    Posts
    2

    Trig identities.

    Hello everyone, I have a couple of questions for you today.

    First, how does one deal with "sinx + sin2x" (or anything for that matter, cosx - cos2x, etc)? Is it "sin3x" or rather sinx + sin(x+x) and then expand the sin(x+x) into sinxcosx+cosxsinx?

    An Identity to fit the question,

    (sinx-sin3x)/(cosx+cos3x) = -tanx
    _____________________________

    Also, this question on my review homework seems to be ridiculous, and no one in my class can seem to get it.

    (sinx+siny)/(cosx-cosy) = -cot(x/2 - y/2)

    May I also mention, we can not use the Sum-product identity, cosa + cosb = 2cos(-------,

    Thank you
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Aug 2007
    From
    USA
    Posts
    3,110
    Thanks
    2
    You have the right idea. Changing an odd "2x" function to a bunch of 'x' functions should be beneficial.

    For that last one, there MUST be a clue in the expansion of tan(A+B).
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Trig Identities
    Posted in the Calculus Forum
    Replies: 2
    Last Post: December 3rd 2009, 06:44 AM
  2. Trig identities
    Posted in the Trigonometry Forum
    Replies: 6
    Last Post: June 22nd 2009, 06:58 AM
  3. Trig Identities
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: November 9th 2008, 04:35 PM
  4. Trig Identities
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: November 7th 2008, 08:25 PM
  5. Trig Identities Help!!!!
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: April 14th 2008, 11:47 AM

Search Tags


/mathhelpforum @mathhelpforum