Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    3
    ReputationRep:
    Hi ppl,

    There are two proofs which I cannot seem to follow through.

    sin(x) = 2tan(x/2)/1+tan^2(x/2)

    cos(x) = 1-tan^2(x/2)/1+tan^(x/2)

    Some detailed derivation will be appreciated.

    Thanks

    Edit: Figured out cos(x)
    Offline

    1
    ReputationRep:
    How far do you manage to get? it may help if you post where you get to and how you got there, then we can say what point you either went wrong or what you should try next.
    • Thread Starter
    Offline

    3
    ReputationRep:
    (Original post by Lakura225)
    How far do you manage to get? it may help if you post where you get to and how you got there, then we can say what point you either went wrong or what you should try next.
    For sinx, I don't know where to start it.

    For cosx, I don't know if I have done a valid method but did figure it out after posting.

    cosx = cos^(x/2) - sin^2(x/2) <= cos(x/2 +x/2)

    = 1/sec^(x/2) - sin^2(x/2)

    Making the same denominator: = 1 - tan^2(x/2)/1+tan^(x/2)
    Offline

    19
    ReputationRep:
    (Original post by mathsRus)
    For sinx, I don't know where to start it.

    For cosx, I don't know if I have done a valid method but did figure it out after posting.

    cosx = cos^(x/2) - sin^2(x/2) <= cos(x/2 +x/2)

    = 1/sec^(x/2) - sin^2(x/2)

    Making the same denominator: = 1 - tan^2(x/2)/1+tan^(x/2)
    look at Q 246 on the link

    http://madasmaths.com/archive/maths_..._questions.pdf

    sorry the download time is around 5 minutes

    (around 400 trig questions with solutions)

    (Apologies that the booklet is currently under construction, I was physically working on it when I saw your message.)
    Offline

    1
    ReputationRep:
    This site might help you when you get stuck, i got lazy and couldn't be bothered to find my identities :P

    http://www.symbolab.com/solver/trigo...?origin=button
    • Thread Starter
    Offline

    3
    ReputationRep:
    (Original post by TeeEm)
    look at Q 246 on the link

    http://madasmaths.com/archive/maths_..._questions.pdf

    sorry the download time is around 5 minutes

    (around 400 trig questions with solutions)

    (Apologies that the booklet is currently under construction, I was physically working on it when I saw your message.)
    Thanks again, I have test on Monday so hopefully I will go over what I can.

    Also what do those (****) mean?
    Offline

    19
    ReputationRep:
    (Original post by mathsRus)

    Also what do those (****) mean?
    difficulty 4 star.
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Has a teacher ever helped you cheat?
    Useful resources

    Make your revision easier

    Maths

    Maths Forum posting guidelines

    Not sure where to post? Read the updated guidelines here

    Equations

    How to use LaTex

    Writing equations the easy way

    Student revising

    Study habits of A* students

    Top tips from students who have already aced their exams

    Study Planner

    Create your own Study Planner

    Never miss a deadline again

    Polling station sign

    Thinking about a maths degree?

    Chat with other maths applicants

    Can you help? Study help unanswered threads

    Groups associated with this forum:

    View associated groups
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Write a reply...
    Reply
    Hide
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.