1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What am I doing wrong?

  1. Jul 6, 2005 #1
    Hello

    I have to prove that

    (cos 3x - Cos 7x) / (Sin 3x + Sin 7x) = Tan 2x

    So this is what I am doing

    -2 Sin (3x + 7x)/2 Sin (3x-7x)/2
    --------------------------------
    2 Sin (3x + 7x)/2 Cos (3x-7x)/2

    -2 Sin 5x Sin -2x
    -----------------
    2 Sin 5x Cos -2x

    Sin 2x
    -------
    -cos 2x

    Which equals -Tan 2x. What am i doing wrong??

    Thanks
     
  2. jcsd
  3. Jul 6, 2005 #2
    Cos(-2x)=Cos(2x)
    Then i believe everything is ok.
     
  4. Jul 6, 2005 #3
    Thanks for your help.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: What am I doing wrong?
  1. What am i doing wrong (Replies: 2)

  2. What am I doing wrong? (Replies: 6)

Loading...