Results 1 to 5 of 5

Math Help - Trig proof - urg

  1. #1
    Member
    Joined
    May 2008
    Posts
    150
    Awards
    1

    Trig proof - urg

    It is given that:
    <br />
Sin7\theta = 7Sin{\theta} - 56Sin^3\theta + 112Sin^5\theta - 64Sin^7\theta<br />

    Hence, prove that the only real solution of the equation
    Sin 7 \theta = 7Sin\theta
    are given by
    <br />
\theta = n\pi<br />
    Where n is an integer.
    I am really stuck with this

    Any help would be greatly appreciated.
    Thankyou.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Junior Member bebrave's Avatar
    Joined
    Apr 2009
    Posts
    29
    Math Forum - Ask Dr. Math
    this link can help you
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    May 2008
    Posts
    150
    Awards
    1
    Quote Originally Posted by bebrave View Post
    Math Forum - Ask Dr. Math
    this link can help you
    Thankyou very much for your reply however im find with putting Sin 7x into the equation by demoivres , that was the first part of the question which i managed ...its the proof part im struggling with .
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,969
    Thanks
    1789
    Awards
    1
    Use what you just proved. Substitute , substract 7\sin(\theta).
    You then have 64\sin^7(\theta)-112\sin^5(\theta)+56\sin^3(\theta)=0.
    Show that has no real roots other than 0.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Member
    Joined
    May 2008
    Posts
    150
    Awards
    1
    Quote Originally Posted by Plato View Post
    Use what you just proved. Substitute , substract 7\sin(\theta).
    You then have 64\sin^7(\theta)-112\sin^5(\theta)+56\sin^3(\theta)=0.
    Show that has no real roots other than 0.
    Plato, you're awsome! Thanks again for another reply
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. trig proof help
    Posted in the Trigonometry Forum
    Replies: 9
    Last Post: December 13th 2011, 09:03 AM
  2. [SOLVED] Trig Proof
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: August 28th 2010, 04:38 PM
  3. trig proof
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: May 16th 2010, 06:55 AM
  4. Trig Lab Proof
    Posted in the Trigonometry Forum
    Replies: 3
    Last Post: February 10th 2010, 12:11 PM
  5. Help with a Trig Proof
    Posted in the Calculus Forum
    Replies: 1
    Last Post: October 11th 2008, 12:16 PM

Search Tags


/mathhelpforum @mathhelpforum