Hey! Sign in to get help with your study questionsNew here? Join for free to post

arrggh! newton-raphson nightmare, textbook mistakes?!?!

Announcements Posted on
Fancy a fiver? Fill in our quick survey and we’ll send you a £5 Amazon voucher 03-05-2016
Talking about ISA/EMPA specifics is against our guidelines - read more here 28-04-2016
  1. Offline

    ReputationRep:
    the equation in question is 3sin(x+3)=cos(2x) to 4 dp between 0 =< x =< 7

    by rearranging the equation i get f(x) = 3sin(x+3)-cos(2x) which im sure is correct as this is what i get in maple and calculus bagatirx

    next step is to check by basically guess

    so I guess 3.5 which is -0.10854 and 3.75 is 1.0034 so i think ok jackpot I'm close enough

    anyway I differentiate it to 3COS(x+3) + 2sin(2x)

    I then calculator using general iteration formula which is xnew= x(-0.10854) - f(x)/f'(x)

    I run this continually until i get -0.1765 and this is what the newton-raphson calculator online confirms it as

    my book states the answer is 3.524 and 6.1067 I MEAN WTF IS THAT??!! is my answer wrong, am I doing something wrong?

    or is my book full of **** (which it has been lately, alot of stuff is incorrect but I can't rule it out that I haven't made a mistake or whether the fact the book is wrong)
  2. Offline

    ReputationRep:
    I think there's a root at -0.1765, although that root isn't in the domain 0 ≤ x ≤ 7. I got 6.1067, but not 3.524. I don't understand how you can have two values, so I too am confused by your textbook. o.o
  3. Offline

    ReputationRep:
    The book is correct mate. Go over your working again.
  4. Offline

    ReputationRep:
    ok i figured it out, i was using the wrong value for x when it came to using the iteration formula
  5. Offline

    ReputationRep:
    You need to do 3.5-F(3.5)/F'(3.5) to begin with. Then go from there.

Reply

Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. Oops, you need to agree to our Ts&Cs to register
  2. Slide to join now Processing…

Updated: June 19, 2012
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Today on TSR

When it's all over...

How will you celebrate when your last exam is done?

Poll
How often are people with Asthma hospitalised in the UK?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read here first

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
Study resources
Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.