Results 1 to 2 of 2

Math Help - Some proofs i got stuck on

  1. #1
    Newbie
    Joined
    Mar 2011
    Posts
    8

    Some proofs i got stuck on

    Prove (sin2x+sinx)/(cos2x+cosx+1)=tanx
    I have tried to sub in cos˛x+sin˛x=1 for 1 and then cancelling but that wouldnt work. I think you need to convert the sinx/cosx into tanx but im still not sure.

    Prove (sec-tan)˛=(1-sin)/(1+sin)
    Another one i got stuck on. I tried to start with the LHS but wasnt sure whether to expand the brackets ot to turn sec into 1/cos and then turn the tan into sin/cos which would make a common denominator. However the ˛ is still there and I have no idea what to do with that haha

    Any help would be appreciated, even just an idea for a start would be good

    Thankyou
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,697
    Thanks
    1512
    For the first, you need to use the identities \displaystyle \sin{2x} \equiv 2\sin{x}\cos{x} and \displaystyle \cos{2x} \equiv 2\cos^2{x} - 1. See what you can do after you've done that...

    For the second, try working on the RHS. Start by multiplying top and bottom of the RHS by \displaystyle 1 - \sin{\delta}.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 1
    Last Post: February 21st 2011, 10:12 AM
  2. Stuck on Proofs question
    Posted in the Discrete Math Forum
    Replies: 2
    Last Post: April 7th 2009, 07:10 PM
  3. Proofs
    Posted in the Discrete Math Forum
    Replies: 1
    Last Post: October 17th 2008, 04:39 PM
  4. Replies: 3
    Last Post: October 6th 2007, 02:01 PM
  5. Stuck, Stuck, Stuck - Need Help Urgently
    Posted in the Algebra Forum
    Replies: 3
    Last Post: May 17th 2005, 05:46 AM

Search Tags


/mathhelpforum @mathhelpforum