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!

Trig identity Q

  1. Aug 16, 2007 #1

    T-7

    User Avatar

    Could someone tell me which trig identity this chap (in a Physics textbook) is using to turn

    sin(Kx)sin(2Kx)

    into

    sin^2(3Kx/2) - sin^2(Kx/2)

    Cheers.
     
  2. jcsd
  3. Aug 16, 2007 #2
    [tex]\sin{kx}\sin{2kx}[/tex]

    [tex]=\frac{\cos{(-kx)}-\cos{(3kx)}}{2}[/tex]

    [tex]=\frac{\cos{(kx)}}{2} - \frac{\cos{(3kx)}}{2} [/tex]

    [tex]=\frac{-1 + \cos{(kx)}}{2} - \frac{-1 + \cos{(3kx)}}{2}[/tex]

    [tex]=\sin^2{(3kx/2) - \sin^2{(kx/2)}[/tex]
     
  4. Aug 16, 2007 #3

    T-7

    User Avatar

    Ah... Thank you very much.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Trig identity Q
  1. Trig identities (Replies: 12)

  2. Trig identity (Replies: 4)

  3. Trig identities (Replies: 3)

  4. Trig Identity (Replies: 4)

  5. Trig Identities (Replies: 3)

Loading...