Turn on thread page Beta
    • Thread Starter
    Offline

    0
    ReputationRep:
    Basically what it says above. I just cant crack it for some reason, ive tried opening up the bracket which makes it worse. Ive also tried changing the cos2x to 1-2sin^2x and 2cos^2x-1 which still doesnt get me anywhere.

    Thanks
    Offline

    17
    ReputationRep:
    (Original post by Ramin Gorji)
    Basically what it says above. I just cant crack it for some reason, ive tried opening up the bracket which makes it worse. Ive also tried changing the cos2x to 1-2sin^2x and 2cos^2x-1 which still doesnt get me anywhere.

    Thanks
    Expanding the brackets is probably the best idea, and recalling that \cos 4x = 2\cos ^22x - 1 will be useful.
    Offline

    18
    ReputationRep:
    Well, for simplicity, let u = 2x.

    So we're trying to integrate (cosu - 1)^2 = cos^2u - 2cosu + 1

    Well, -2cosu + 1 = -2cos(2x) + 1 is trivial to integrate.

    What about this cos^2u guy? Well, how do you integrate cos^2x in general? Do the same method but write u instead of x, remembering to convert all the u terms back into x before integrating.
    Offline

    9
    ReputationRep:
    Surely cos2x-1 is 1-2(sinx^2) - 1, which is -2(sinx^2)?
    Square that and you'll get 4(sinx^4), goes as follows (minus the 4): http://answers.yahoo.com/question/in...5170410AA0eFMZ
    • PS Helper
    Offline

    14
    PS Helper
    (Original post by dragonmeister)
    Surely cos2x-1 is 1-2(sinx^2) - 1, which is -2(sinx^2)?
    Square that and you'll get 4(sinx^4), goes as follows (minus the 4): http://answers.yahoo.com/question/in...5170410AA0eFMZ
    You realise that solution put it back in terms of \cos 2x again before proceeding? [And then it followed what Farhan/Swayum did.]
    Offline

    2
    ReputationRep:
    (Original post by Swayum)
    Well, for simplicity, let u = 2x.

    So we're trying to integrate (cosu - 1)^2 = cos^2u - 2cosu + 1

    Well, -2cosu + 1 = -2cos(2x) + 1 is trivial to integrate.

    What about this cos^2u guy? Well, how do you integrate cos^2x in general? Do the same method but write u instead of x, remembering to convert all the u terms back into x before integrating.
    Can you show your working out please? Because I don't understand what you're saying. :dontknow:
    Offline

    19
    ReputationRep:
    (Original post by Scopeowner)
    Can you show your working out please? Because I don't understand what you're saying. :dontknow:
    very optimistic to expect an answer after 4 years ...
    • PS Reviewer
    Offline

    20
    ReputationRep:
    PS Reviewer
    Yeah I'm gonna close this thread.
 
 
 
Turn on thread page Beta
Updated: October 14, 2015

University open days

  1. University of Edinburgh
    All Departments Undergraduate
    Sat, 22 Sep '18
  2. University of Exeter
    Undergraduate Open Days - Penryn Campus Undergraduate
    Sat, 22 Sep '18
  3. Loughborough University
    General Open Day Undergraduate
    Sat, 22 Sep '18
Poll
Which accompaniment is best?
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.