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1. C3 Iteration (Which initial x value to use?)
In Ch. 4 of Edexcel C3, sometimes you have to choose your own value of x-zero.

So I tried using values that were close to the root that I knew the equation had, but this only gave me the positive root, and I need the negative root.

So when you are not given an initial x-zero value, what do you do?

Thanks
2. Re: C3 Iteration (Which initial x value to use?)
hmmm, in AQA we are always given a starting point

do you not usually have a part(a) asking you to show that a root is in a given interval so that you can use one end or the middle of that interval
3. Re: C3 Iteration (Which initial x value to use?)
(Original post by Citrus_lime)
In Ch. 4 of Edexcel C3, sometimes you have to choose your own value of x-zero.

So I tried using values that were close to the root that I knew the equation had, but this only gave me the positive root, and I need the negative root.

So when you are not given an initial x-zero value, what do you do?

Thanks
Ch 4 is the iteration chapter, in this there are also some question in which we have to choose our own iteration formula, though such question will be unlikely in an exam.

(Original post by TenOfThem)
hmmm, in AQA we are always given a starting point

do you not usually have a part(a) asking you to show that a root is in a given interval so that you can use one end or the middle of that interval
The book contains a variety of questions some of which don't match with the ones in the exam.
4. Re: C3 Iteration (Which initial x value to use?)
(Original post by raheem94)
The book contains a variety of questions some of which don't match with the ones in the exam.
Ah

yes the AQA syllabus includes choosing the formula and the starting point as teaching elements but is clear that this is not required in the exam
5. Re: C3 Iteration (Which initial x value to use?)
normally you get something like 1.9284 for example and you have to choose 1.92845 and 1.92835 and that gives a positive and negative . basically upper and lower bounds.
6. Re: C3 Iteration (Which initial x value to use?)
(Original post by AndrewJames)
normally you get something like 1.9284 for example and you have to choose 1.92845 and 1.92835 and that gives a positive and negative . basically upper and lower bounds.

They are all +ve

The OP is looking for a -ve root ... not a negative value for f(x)
7. Re: C3 Iteration (Which initial x value to use?)
(Original post by AndrewJames)
normally you get something like 1.9284 for example and you have to choose 1.92845 and 1.92835 and that gives a positive and negative . basically upper and lower bounds.
This method is used to prove that the root is correct to 4 significant figures not to find the root.
8. Re: C3 Iteration (Which initial x value to use?)
(Original post by TenOfThem)

They are all +ve

The OP is looking for a -ve root ... not a negative value for f(x)
sorry may have misunderstood might be easier to see the question?
9. Re: C3 Iteration (Which initial x value to use?)
(Original post by Citrus_lime)
In Ch. 4 of Edexcel C3, sometimes you have to choose your own value of x-zero.

So I tried using values that were close to the root that I knew the equation had, but this only gave me the positive root, and I need the negative root.

So when you are not given an initial x-zero value, what do you do?

Thanks
Wondered if you got the ans. you were loooking for