Results 1 to 2 of 2

Math Help - Trigo-equation

  1. #1
    Newbie SADANE ANTAR's Avatar
    Joined
    Dec 2009
    Posts
    4

    Trigo-equation

    Solve in R :
     <br />
4(\cos ^{4}(x)+\sin ^{4}(x))=7\cos (2x+\frac{\pi }{6})\cos (2x-\frac{\pi }{6})<br />
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Sep 2008
    From
    West Malaysia
    Posts
    1,261
    Quote Originally Posted by SADANE ANTAR View Post
    Solve in R :
     <br />
4(\cos ^{4}(x)+\sin ^{4}(x))=7\cos (2x+\frac{\pi }{6})\cos (2x-\frac{\pi }{6})<br />
    HI

    4(\cos^4 x+\sin^4 x)=7\cos (2x+30)\cos (2x-30)

    4[(\cos^2 x+\sin^2 x)^2-\frac{1}{2}(4\cos^2 x\sin^2 x)]= [tex]7{\frac{1}{2}[\cos (2x+30+2x-30)+\cos (2x+30-2x+30)]}[\MATH]

    4(1-\frac{1}{2}\sin^2 2x)=\frac{7}{2}(\cos 4x+\frac{1}{2})

    4-2\sin^2 2x =\frac{7}{2}[\cos 2(2x)+\frac{1}{2}]

    8-4\sin^2 2x=7(1-2\sin^2 2x+\frac{1}{2})

    16-8\sin^2 2x=21-14\sin^2 2x

    Solve \sin 2x=\sqrt{\frac{5}{6}}
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. trigo equation
    Posted in the Trigonometry Forum
    Replies: 3
    Last Post: December 19th 2009, 11:16 AM
  2. New Trigo-equation
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: December 17th 2009, 04:36 PM
  3. Tan : Trigo-equation
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: December 16th 2009, 08:10 AM
  4. trigo and log equation
    Posted in the Trigonometry Forum
    Replies: 5
    Last Post: June 9th 2009, 09:30 AM
  5. trigo equation
    Posted in the Trigonometry Forum
    Replies: 7
    Last Post: September 11th 2008, 06:07 AM

Search Tags


/mathhelpforum @mathhelpforum