You are Here: Home

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

Announcements Posted on
Talking about ISA/EMPA specifics is against our guidelines - read more here 28-04-2016
1. 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. 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. The book is correct mate. Go over your working again.
4. ok i figured it out, i was using the wrong value for x when it came to using the iteration formula
5. You need to do 3.5-F(3.5)/F'(3.5) to begin with. Then go from there.

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
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

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.

This forum is supported by:
Today on TSR

### How to predict exam questions

No crystal ball required

Poll
Useful resources

## Make your revision easier

### Maths Forum posting guidelines

Not sure where to post? Read here first

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams

Can you help? Study help unanswered threads

## Groups associated with this forum:

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