1. Not finding help here? Sign up for a free 30min 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!

Proving Trigonometric Identities

  1. Apr 24, 2009 #1
    1. The problem statement, all variables and given/known data
    1) sin(x+y)sin(x-y)=cos^2y-cos^2x

    2) tan(∏⁄4+x)+tan(∏/4-x)=2sec2x

    3) cosx-cosy=-2sin(x+y/2)sin(x+y/2)

    4) 2cotx-2tanx=4-2sec^2x/tanx


    2. Relevant equations
    all trig identities


    3. The attempt at a solution
    1) i understand that i should show what i have attempted but there is way too many lines of manipulating the equations and i don't have the time to write it down. i can say that for all of these identities i have changed them to cos and sin as these can be the easiest to solve and then used trig identities to make both sides look the same. i have nt had any luck with these and i was hoping you guys could help me

    thx alot!
     
  2. jcsd
  3. Apr 24, 2009 #2
    Is it (x+y)/2 or x+(y/2)?
    Again... is it (4-2sec^2x)/tanx or 4-(2sec^2x/tanx)?
    Sorry, you'll have to make time to write what you have so far if you want us to help. I'll give you one suggestion -- in #2, don't convert to cosines and sines as your first step. Too messy. Instead, use the tangent sum & difference formulas.


    01
     
    Last edited: Apr 25, 2009
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Proving Trigonometric Identities
Loading...