Results 1 to 2 of 2

Math Help - Trig Proof Help

  1. #1
    Newbie
    Joined
    Dec 2006
    Posts
    4

    Trig Proof Help

    Hi

    I have the task of constructing a proof that shows how sinx/2 can be equal to plus or minus root((1-cosx)/2). Also how cosx/2 = plus or minus root((1+cosx)/2). I've been given the hint that it would involve the fact that sinx = plus or minus root((1-cos2x)/2) and cos2x = 1-2sin^2x. Any help I could get would be appreciated.

    Edit: Here is a slight clarification if I typed poorly.

    Proofs for:

    and

    Last edited by Kolbeck10; February 19th 2007 at 12:59 PM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,678
    Thanks
    611
    Hello, Kolbeck10!

    The problem is strangely worded . . .
    I'm not sure exactly how we should construct the proofs.


    I have the task of constructing a proof that:
    . . [1] sin(x/2) = ± sqrt[(1 - cos x)/2]
    . . [2] cos(x/2) = ± sqrt[(1 + cos x)/2]


    I've been given the hint that it would involve the fact that:

    . . (a) sin x .= .± sqrt[(1 - cos2x)/2] .and

    . . (b) cos2x .= .1 - 2sin²x

    They actually gave us hint (a) ??

    Just replace x with x/2

    . . and we have: .sin(x/2) .= .± sqrt[(1 - cos x)/2] .
    . . . wow, that was hard!


    I don't know why they gave us hint (b).
    . . It's the same as hint (a).

    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. [SOLVED] Trig Proof
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: August 28th 2010, 03:38 PM
  2. trig proof
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: May 16th 2010, 05:55 AM
  3. Trig Lab Proof
    Posted in the Trigonometry Forum
    Replies: 3
    Last Post: February 10th 2010, 11:11 AM
  4. Trig proof - urg
    Posted in the Trigonometry Forum
    Replies: 4
    Last Post: May 13th 2009, 06:57 AM
  5. Help with a Trig Proof
    Posted in the Calculus Forum
    Replies: 1
    Last Post: October 11th 2008, 11:16 AM

Search Tags


/mathhelpforum @mathhelpforum