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!

Why sinxcos2x = (sin3x - sinx)*0.5

  1. Apr 12, 2009 #1
    can someone please show me why sinxcos2x = (sin3x - sinx)*0.5

    I've been working on it for thirty minutes
     
  2. jcsd
  3. Apr 12, 2009 #2
    Re: sinxcos2x

    can u expand sin(3x) ?? and cos(2x)

    just simplify both sides..and u'll get it..
     
  4. Apr 12, 2009 #3
    Re: sinxcos2x

    You should use the identities

    [tex]\cos{2\theta} = 1-2\sin^2{\theta}[/tex]

    [tex]\sin{3\theta} = 3\sin{\theta} - 4\sin^3{\theta}[/tex]

    Perhaps you were putting these identities in terms of cosines. When possible, stick with as few trig functions as possible and replace the [tex]\cos^2{\theta}[/tex] with [tex]1-\sin^2{\theta}[/tex] or vice versa.
     
    Last edited: Apr 12, 2009
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Why sinxcos2x = (sin3x - sinx)*0.5
  1. Limit of sin2x/sin3x (Replies: 10)

Loading...