Hey there Sign in to join this conversationNew here? Join for free

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

Announcements Posted on
    • Thread Starter
    • 0 followers
    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)
    • 3 followers
    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
    • 1 follower
    Offline

    ReputationRep:
    The book is correct mate. Go over your working again.
    • Thread Starter
    • 0 followers
    Offline

    ReputationRep:
    ok i figured it out, i was using the wrong value for x when it came to using the iteration formula
    • 1 follower
    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?

    this is what you'll be called on TSR

  2. this can't be left blank
    this email is already registered. Forgotten your password?

    never shared and never spammed

  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. By joining you agree to our Ts and Cs, privacy policy and site rules

  2. Slide the button to the right to create your account

    Slide to join now Processing…

Updated: June 19, 2012
New on TSR

Moving on from GCSEs

What advice would you give someone starting A-levels?

Article updates
Reputation gems:
You get these gems as you gain rep from other members for making good contributions and giving helpful advice.