Results 1 to 2 of 2

Math Help - Can someone please help with these trig problems?

  1. #1
    Newbie
    Joined
    Oct 2009
    Posts
    1

    Can someone please help with these trig problems?

    I need to fine the exact value of these problems. Thank you!

    1) cos(2 cos^-1 4/5)

    2) cos [2 tan^-1 (-4/3)]
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Member
    Joined
    May 2009
    From
    New Delhi
    Posts
    153
    Quote Originally Posted by onoitsvi View Post
    I need to fine the exact value of these problems. Thank you!

    1) cos(2 cos^-1 4/5)

    2) cos [2 tan^-1 (-4/3)]
    1) cos(2 cos^-1 4/5)
     let\ \cos^{-1} \left (\frac{4}{5}\right )=x \quad \Rightarrow \cos x= \frac{4}{5} \quad ..............(1)

    \therefore \cos\left (2 \cos^{-1} {\frac{4}{5}}\right ) =\cos (2x)=2\cos^2x-1
    substitute value of cos x from (1) and solve
    2) cos [2 tan^-1 (-4/3)]
    let \tan^{-1} \left (\frac{-4}{3}\right )= x \quad \Rightarrow \tan x=\frac{-4}{3} \quad ..............(2)
    \therefore \cos \left \{2 \tan^{-1} \left ( \frac{-4}{3} \right )\right \}= \cos(2x)= \frac{1-tan^2x}{1+tan^2x}
    substitute value of tan x from (2) and solve
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. trig problems:
    Posted in the Trigonometry Forum
    Replies: 4
    Last Post: November 2nd 2010, 12:16 AM
  2. Replies: 7
    Last Post: April 15th 2010, 09:12 PM
  3. 2 trig problems pls help...
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: October 15th 2008, 02:28 PM
  4. Some trig problems from Shy Guy
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: April 16th 2008, 04:53 AM
  5. Some trig problems =/
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: December 20th 2006, 04:31 PM

Search Tags


/mathhelpforum @mathhelpforum