You are Here: Home >< Maths

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

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.

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:
Updated: June 19, 2012
Today on TSR

### Should I ask for his number?

Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• Poll
Useful resources

## Make your revision easier

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### 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
Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• 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