Results 1 to 2 of 2

Math Help - Double Angle Help

  1. #1
    Newbie
    Joined
    Aug 2009
    Posts
    1

    Double Angle Help

    Can someone walk me through the following problem:

    Find sin2(x) , cos2(x), and tan2(x) if cos(x) = -3/[(13)^(1/2)] and x terminates in quadrant II

    Thank You.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    A riddle wrapped in an enigma
    masters's Avatar
    Joined
    Jan 2008
    From
    Big Stone Gap, Virginia
    Posts
    2,551
    Thanks
    12
    Awards
    1
    Quote Originally Posted by super View Post
    Can someone walk me through the following problem:

    Find sin2(x) , cos2(x), and tan2(x) if cos(x) = -3/[(13)^(1/2)] and x terminates in quadrant II

    Thank You.
    Hi super,

    Since \cos X = \frac{-3}{\sqrt{13}}, this means that x = -3 and r=\sqrt{13}.

    Using r^2=x^2+y^2, you can determine that y=2.


    This would make \sin X = \frac{2}{\sqrt{13}}

    Note that \sin 2X = 2\sin X \cos X

    Substituting, we arrive at \sin 2X=2\left(\frac{2}{\sqrt{13}}\right)\left(\frac{-3}{\sqrt{13}}\right)=-\frac{12}{13}.

    Use the double angle identities for \cos 2X and \tan 2X to complete your assignment.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Simplify the Expression (Double-Angle or Half-Angle)
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: November 3rd 2009, 03:38 PM
  2. More double angle and Half angle problems
    Posted in the Trigonometry Forum
    Replies: 5
    Last Post: July 21st 2009, 06:54 PM
  3. Half angle or double angle Identities
    Posted in the Trigonometry Forum
    Replies: 4
    Last Post: July 21st 2009, 05:20 PM
  4. Help with double angle and half angle formulas
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: April 20th 2009, 05:30 PM
  5. Replies: 2
    Last Post: February 15th 2007, 10:16 PM

Search Tags


/mathhelpforum @mathhelpforum