FP1 Newton Raphson

f(x) = x^3 - 3x - 6
Use the Newton Raphson process to find the positive root of this equation correct to 2 d..
f(2) = -4
f(3) = 12 so root implies in [2,3]
My question is does it matter if i let Xo = 2, or Xo = 3.
I did Xo = 3 but i got the wrong answer from the solution bank as the solution bank did Xo = 2. Can anyone help me ? thanks

I always hated Newton-Raphson

Did it specify in the question whether to use x_o = 2 or 3?

Otherwise I'd say if you can tell it's diverging, try the other limit.

@Zacken correct me if I'm wrong

It doesn't diverge, the OP is just doing it wrong.

x_0 = 3 is a good starting value, won't make it diverge.

Oh okay.. Does x_0 = 2 diverge either?

Cause I remember sometimes the upper limit would diverge bu the lower wouldn't and vice-versa. It was weird definitely did not deserve my FP1 mark xD

Nopes, converges quadratically for both $x_0 = 2$ and $x_0 = 3$.

ok thanks for solving my first question. I think i didnt make any mistake and i let Xo = 3 and i got 2.36 to 2 d.p.. But the answer in solution bank is 2.28 to 2 d.p.

The solution bank is incorrect, you are correct.

ok thankyou so much

ok thanks for solving my first question. I think i didnt make any mistake and i let Xo = 3 and i got 2.36 to 2 d.p.. But the answer in solution bank is 2.28 to 2 d.p.

Was the question to apply the NRM only once?

Using $x_0 = 2$:

$x_1 = 2.444444444...$

$x_2 = 2.35916...$

Using $x_0 = 3$:

$x_1 = 2.5$

$x_2 = 2.36508...$

So, nowhere does it show 2.28, think we can assume the solution bank is just completely wrong here.

By the way, nobody has replied to my S2 answers yet, this is hilarious.

Haha I hadn't actually calculated, but you do lose marks if you give a more accurate answer in the real exam which is why I was asking. Thanks for confirming!

Now I really wish I got S2 over with this session; I will have no one to discuss with post exam plus a clash with FP3 to deal with.

Did you find out if it's actually dangerous to post answers 2 hours after the exam? I always thought IALs were taken roughly at the same time. I didn't even know countries left of the Greenwich median took IAL exams, I always thought they were targeted towards a more "Eastern" audience.

Neither did I, tbh, I just shoved it into Wolfram and it did it for me.

Argh, yeah, I think you'd have managed doing it in Jan quite well. Although, I suspect the only reason why it's unpopular is because it's Jan. I think there'll be a lot more people doing it in June, so you can discuss your answers then. Although the FP3 clash is horrible...

Nopes, I'm not too bothered, to be honest. The number of candidates who are left of GMT intersected with those on TSR intersected with those looking at the thread a few hours before the exam is likely to be zero or minuscule anyway. I thought IAL was always east as well, it could possibly be.

I didn't give C34 or S2 in January for a trivial reason, it's quite embarrassing.
I could discuss my answers then, but there's hardly anyone doing IAL here and your answers are easily the most trustable! At least you'll be there for F2, F3, Physics and I hope S3!

Yeah, I agree with that. It really doesn't seem very likely.

What are you going to do with this break?