How to calculate order and error of the bisection method?

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I have a problem understanding 3 (related) things here. First attachment:

formula order bisection

1) Let's say (a) would be the line in the screenshot "error = current root - actual", and (b) the next line with en+1= M*en^(alpha). How to come from (a) to (b)? 2) What is meant in (a) by "current root" and "actual"? If I have a function f(x) = sin(cos(e^x)) in an interval [0,1], how to calculate the error concretely in this example, according to this formula? I mean how to applicate the formula on this function?

And here for these errors attached (2nd attachment):

enter image description here

3) How to calculate for example e1, e2 and e3 for a given function? Let's say if I take the function f(x) in my example above.

And last, for the Nr. of iteration formula here (3rd attachment):

enter image description here

  1. Why is it said on the beginning (first screenshot), that error = "current root" - "actual" and now "epsilon" = (b-a)/2^n? Are we talking about the same error? Does it just have two formulas?
  2. And if so, what's the relationship between the error going by (1/2) and the formula "epsilon" = (b-a)/2^n? If it would had been quadratic, would the formula be: "epsilon" = (b-a)/2^(n^2)?

I am having the last chance in my exam, so any help is really welcome! Thank you very much in advance!

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The organization of your quotes is dubious. The general concept of the first image is not applicable to the bisection method. While the interval length $ε_n$ of the bisection method shrinks with a constant geometric rate of $\frac12$, the distance $e_n$ of the last midpoint to the actual solution can jump erratically, always a fraction of the interval length $e_n\le ε_n$, but not necessary with a limit of the ratio $\frac{e_n}{ε_n}$.

The example sequence is also not very useful, as it looks more like an almost constant sequence than anything that converges to zero.