High School Representation of infinitesimals in different ways

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There are four primary types of infinitesimals: 1) dx=1/N, where N represents the cardinality of natural numbers; 2) Hyperreal numbers, defined as ε=1/ω, with ω being larger than any real number; 3) Surreal numbers, which include transfinite numbers like ω and infinitesimals like ε; and 4) Nilpotent infinitesimals, characterized by ε²=0. The discussion highlights the various representations of infinitesimals and invites clarification on their differences. Understanding these distinctions is crucial for deeper mathematical comprehension. The conversation emphasizes the complexity and nuances in the representation of infinitesimals.
Mike_bb
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Hello.

There are 4 types of infinitesimals:

1) dx=1/N, N is the number of elemets of the set of the natural numbers (letter N is used to indicate the cardinality of the set of natural numbers)

2) Hyperreal numbers: ε=1/ω, ω is number greater than any real number.

3) Surreal numbers: { 0, 1, 2, 3, ... | } = ω , { 0 | 1, 1/2, 1/4, 1/8, ...} = ε, where ω is a transfinite number greater than all integers and ε is an infinitesimal greater than 0 but less than any positive real number.

4) Nilpotent infinitesimals are numbers ε where ε2 = 0

Infinitesimals are represented in different ways. What is difference between them?

Thanks.
 
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Mike_bb said:
Infinitesimals are represented in different ways. What is difference between them?
An infinitesimal difference, perhaps?
 
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PeroK said:
An infinitesimal difference, perhaps?
Yes
 
There are probably loads of proofs of this online, but I do not want to cheat. Here is my attempt: Convexity says that $$f(\lambda a + (1-\lambda)b) \leq \lambda f(a) + (1-\lambda) f(b)$$ $$f(b + \lambda(a-b)) \leq f(b) + \lambda (f(a) - f(b))$$ We know from the intermediate value theorem that there exists a ##c \in (b,a)## such that $$\frac{f(a) - f(b)}{a-b} = f'(c).$$ Hence $$f(b + \lambda(a-b)) \leq f(b) + \lambda (a - b) f'(c))$$ $$\frac{f(b + \lambda(a-b)) - f(b)}{\lambda(a-b)}...

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