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!

Homework Help: Half angle formula,

  1. Dec 20, 2009 #1
    1. The problem statement, all variables and given/known data

    Can someone please explain how my book got [itex] sin^{2} \theta = \frac{1-cos2\theta}{2} [/itex] and [itex] cos^{2}\theta = \frac{1+cos2\theta}{2} [/itex]

    As I thought the half angle formula's were [itex] sin \frac{\theta}{2} = \sqrt{\frac{1-cos\theta}{2}} [/itex]

    [itex] cos\frac{\theta}{2} = \sqrt\frac{1+cos\theta}{2}} [/itex]

    So how can it also be the top one's aswell?

  2. jcsd
  3. Dec 20, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Replace θ with 2θ.
  4. Dec 20, 2009 #3

    Oh I see, can't believe I missed that.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook