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# The Official Edexcel C3 Revision Thread! (20/06/05 AM) watch

1. Exam is in 8 days time! Post any questions here....
2. I guess I'll start it off... When using an iterative formula, what do you use as the initial x value (ie: x0)... Can it be on either side of the root? how far from the root can it be?
3. (Original post by ArVi)
I guess I'll start it off... When using an iterative formula, what do you use as the initial x value (ie: x0)... Can it be on either side of the root? how far from the root can it be?
very much depends on the individual situation - not an easy question to answer in general. So trial and error might be best

If you wish to bother, it often helps to draw a graph of y=f(x) and y=x on the same graph and then you can represent the iterative process pictorially.
4. (Original post by ArVi)
I guess I'll start it off... When using an iterative formula, what do you use as the initial x value (ie: x0)... Can it be on either side of the root? how far from the root can it be?
Most times you will be given a starting value (i.e. X0 = 4 or X1 =7)

If not then its best to start to the right of the root and with quite a close value or you'll be there all day! So if the root was 1.7564567 you could start with X0 = 2.

But as i said most times you will get given the value.
5. (Original post by !Laxy!)
If not then its best to start to the right of the root...
There's no reason that this could be true. Often it won't matter where you start from, but for every graph where starting on the right is best there's one where starting on the left is best

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