Turn on thread page Beta
    • Thread Starter
    Offline

    0
    ReputationRep:
    Really stuck on this qu. any help would be much appreciated

    given that f(x) = cot x + 3

    solve f(x) + f '(x) = 0, for 0 < x < 2 pie

    i dont have a clue. i tried adding cot x + 3 to -cosec^2x and tried to make every in cos but failed. what should I do?

    thanks. rep on offer
    Offline

    0
    ReputationRep:
    (Original post by Tommy Jay)
    Really stuck on this qu. any help would be much appreciated

    given that f(x) = cot x + 3

    solve f(x) + f '(x) = 0, for 0 < x < 2 pie

    i dont have a clue. i tried adding cot x + 3 to -cosec^2x and tried to make every in cos but failed. what should I do?

    thanks. rep on offer
    Okay so we have cot(x)+3-cosec^2(x)=0. cos(x)/sin(x)+3-1/sin^2(x)=0. => cos(x)sin(x)+3sin^2(x)-1=0 => cos(x)sin(x)=1-3sin^2(x); at this point I'd be tempted to double both sides then put it all in one trig function type (either sin(x) or cos(x))
    Offline

    2
    ReputationRep:
    (Original post by Tommy Jay)
    Really stuck on this qu. any help would be much appreciated

    given that f(x) = cot x + 3

    solve f(x) + f '(x) = 0, for 0 < x < 2 pie

    i dont have a clue. i tried adding cot x + 3 to -cosec^2x and tried to make every in cos but failed. what should I do?

    thanks. rep on offer
    As cosec^2(x) = 1 + cot^2 (x) , you can substitute.

    So f(x) + f '(x) = cot(x) + 3 - (1 + cot^2(x)) = 0

    So, -1 - cot^2(x) + 3 + cot(x) = 0

    Therefore, cot^2 (x) - cot(x) -2 =0
    Then you factorise which gives you :

    = [cot(x) + 1 ] [cot(x)-2] = 0

    so cot(x) = -1 , cot(x) = 2

    Then you should be able to work it out from there :yes:
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: January 15, 2010
The home of Results and Clearing

2,688

people online now

1,567,000

students helped last year

University open days

  1. SAE Institute
    Animation, Audio, Film, Games, Music, Business, Web Further education
    Thu, 16 Aug '18
  2. Bournemouth University
    Clearing Open Day Undergraduate
    Fri, 17 Aug '18
  3. University of Bolton
    Undergraduate Open Day Undergraduate
    Fri, 17 Aug '18
Poll
Do you want your parents to be with you when you collect your A-level results?
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.