Turn on thread page Beta
    • Thread Starter
    Offline

    0
    ReputationRep:
    Express cos(^5) θ in terms of cosines of multiples of θ.
    What is the method for doing this?
    Offline

    2
    ReputationRep:
    De Moivre's theorem?

    (Admittedly I haven't really done the working for this yet :o:)
    Offline

    13
    ReputationRep:
    Express Cos theta in terms of e, put all that to the power of 5 and use the binomial theorem to expand, then at the end just manipulate it to convert it back to trigonometric terms.
    Offline

    3
    ReputationRep:
    (Original post by You Failed)
    Express Cos theta in terms of e, put all that to the power of 5 and use the binomial theorem to expand, then at the end just manipulate it to convert it back to trigonometric terms.

    I agree this is how you start; it gives cos(5theta) in terms of powers of cos(theta). But in answering this question there will be other powers of cos left - which must be disposed of by expanding things like cos(3theta)
    Offline

    13
    ReputationRep:
    (Original post by ian.slater)
    I agree this is how you start; it gives cos(5theta) in terms of powers of cos(theta). But in answering this question there will be other powers of cos left - which must be disposed of by expanding things like cos(3theta)
    Yeah there will be other powers but like you said, you just expand them and use identities to get rid of them.
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: February 1, 2010
Poll
Cats or dogs?
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

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.