Results 1 to 2 of 2

Math Help - Trig Angles tan2x

  1. #1
    Senior Member
    Joined
    Nov 2008
    Posts
    425

    Trig Angles tan2x

    If cosx=-3/5 and pi<x<3pi/2, find tan2x


    I got tan2x=-16/7

    Is my answer right? or is it tan2x=-24/7?
    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 skeske1234 View Post
    If cosx=-3/5 and pi<x<3pi/2, find tan2x


    I got tan2x=-16/7

    Is my answer right? or is it tan2x=-24/7?
    Hi skeske1234,

    Actually, I got \tan 2x=\frac{24}{7}

    If \cos x =-\frac{3}{5}, then x=-3 and r=5 and y=4

    So, \tan x=-\frac{4}{3}

    \tan 2x=\frac{2 \tan x}{1-\tan^2x}

    \tan 2x=\frac{2(-\frac{4}{3})}{1-(-\frac{4}{3})^2}

    \tan 2x = \frac{2(-\frac{4}{3})}{1-\frac{16}{9}}

    \tan 2x = \frac{-\frac{8}{3}}{-\frac{7}{9}}

    \tan 2x = \frac{24}{7}
    Last edited by masters; April 9th 2009 at 01:07 PM.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Solve: tan2x + tan x = 0
    Posted in the Pre-Calculus Forum
    Replies: 10
    Last Post: February 5th 2013, 08:58 AM
  2. solve 2sec2x-cot2x=tan2x
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: May 29th 2011, 07:33 AM
  3. tan2x
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: December 30th 2009, 01:23 AM
  4. Trig Angles
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: April 9th 2009, 12:59 PM
  5. Trig angles
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: January 29th 2009, 08:24 AM

Search Tags


/mathhelpforum @mathhelpforum