In this article, we shall look at some very basic ideas about the Real Analysis, i.e. the study of the structure of Real Number System. We shall discuss the three axioms that are considered to be satisfied by the set of Real Numbers,
The three axioms are :
- Field Axioms
- Order Axioms
- Completeness Axiom
Field Axioms : The set
(i) Axioms for addition :
- R contains an element 0 such that
- For each
there corresponds an element such that
(ii) Axioms for multiplication :
-
contains an element such that and - If
then there exists an element such that
(iii) The distributive law :
Order Axioms : We define
- Law of Trichotomy – For
only one of the expressions can be true : - Transitivity – For
- Monotone Property for addition – For
- Monotone Property for multiplication – For
We call
Before defining the Completeness Axiom, we shall look at the concept of Boundedness. Here, we shall define a few terms before stating the Completeness Axiom.
Aggregate : Any non empty subset, say
Upper bound : A subset
Lower Bound : A subset
Least Upper Bound : Consider an upper bound
Greatest Lower bound : Consider a lower bound
Example : Let
Boundedness : An aggregate S is bounded if it is both bounded above and bounded below. That is, it must have both an upper bound and a lower bound. For example, any finite set is bounded, the empty set
Note : An aggregate need not have a greatest and a least member to be bounded above or bounded below respectively.
Now being done with the required definition, we state the Completeness Axiom(also called the least upper bound axiom).
” Every non-empty set of Real numbers which is bounded above has a supremum.”
The set R satisfies the Field Axioms, Order Axioms, and the Completeness Axiom. Hence the set of real numbers
Also, the set of rational numbers,
The completeness axiom is a really fundamental and important property of real number systems, as proofs various theorems of calculus, the concepts of maxima and minima, mean-value theorems etc. rely on the completeness property of real numbers.