Results 1 to 3 of 3

Math Help - Trig Equation

  1. #1
    Senior Member
    Joined
    Jul 2008
    Posts
    347

    Post Trig Equation

    Can anyone please show me how to do 2cos2x=7cosx. I have no clue.

    Thanx in advance.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by xwrathbringerx View Post
    Can anyone please show me how to do 2cos2x=7cosx. I have no clue.

    Thanx in advance.
    2 \left( 2 \cos^2 (x) - 1 \right) = 7 \cos (x).

    Now re-arrange into a quadratic in cos x .....
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Sep 2008
    From
    Oregon
    Posts
    58
    cos2x=2(cos^2)x-1 (double angle)...that is how Mr Fantastic got his result.

    Rearranging into a quadratic in cos x should yield...

    (4cosx +1)(cosx -2) = 0

    (4cosx) + 1 = 0 and
    (cosx) - 2 = 0

    ....now solve for x in both
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Compute Trig Function Values, Solve Trig Equation
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: September 8th 2011, 07:00 PM
  2. Trig word problem - solving a trig equation.
    Posted in the Trigonometry Forum
    Replies: 6
    Last Post: March 14th 2011, 07:07 AM
  3. Trig Equation with varied trig functions
    Posted in the Trigonometry Forum
    Replies: 12
    Last Post: April 12th 2010, 10:31 AM
  4. Replies: 1
    Last Post: July 24th 2009, 03:56 AM
  5. Replies: 1
    Last Post: July 24th 2009, 02:29 AM

Search Tags


/mathhelpforum @mathhelpforum