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: Trigonometry expansion

  1. Sep 25, 2013 #1
    1. The problem statement, all variables and given/known data

    We know that sin(2⋅x)=2⋅sin(x)⋅cos(x)and cos(2x)=cos^2(x)−sin^2(x). Use the appropriate formula to expand cos(8x) in terms of one of these two formulas.

    2. Relevant equations

    3. The attempt at a solution
    I am not looking for help with the solution, I just want to know what the question is asking me to do. Is it asking me to sub cos(8x) into these equations like cos(8x) = cos^2(4x) - sin^2(4x)? If not what is it asking me to do?

    Thank You!
  2. jcsd
  3. Sep 25, 2013 #2


    Staff: Mentor

    Yes. Now do the same sort of thing on the cos(4x) and sin(4x) terms.

    Note that the notation cos2(4x) means [cos(4x)]2, and similar for sin2(4x).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted