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: Trig Indentity Help

  1. Jan 23, 2010 #1
    1. The problem statement, all variables and given/known data
    Teacher gave this identity twice to us but the starting position slightly varies.

    Prove sec(2x) - tan(2x) = (cos(x)-sin(x))/(cos(x) + sin(x))

    Prove cos(2x)/(1 + sin(2x)) = tan(pi/4-x)


    2. Relevant equations
    pretty much all trig identities


    3. The attempt at a solution

    I get to (1-sin(2x))/cos(2x) = (cos(x)-sin(x))/(cos(x) + sin(x)) and then I'm stumped.
     
  2. jcsd
  3. Jan 23, 2010 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi Hockeystar! Welcome to PF! :wink:
    ok so far :rolleyes:

    now what is cos(2x) ? :smile:
     
  4. Jan 23, 2010 #3
    cosx - sinx(cosx + sinx). How does that help me cancel out something?
     
  5. Jan 23, 2010 #4

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    You mean (cosx - sinx)(cosx + sinx) …

    It doesn't have to cancel to help :wink:

    think! look at the RHS!
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook