- 1 decade agoFavorite Answer
My dear cousin
Seems that you are not familar to Set theory
Let me introduce you this topic
A set can be interpreted as a bag containing some objects
These objects are called "the elements" of the set.
e.g. Let S be the set of atoms in the whole world, then every single atom is an element of S.
Back to your question,
mathematicians use spectial symbols (N, I, Q, R and C) to show the set of Natural no.s, intergers, Rational no.s, Real no.s and complex no.s.
The expression " a ∈S " means " a is an element of the set S".
k ∈N means k is a natural no.
k ∈I means k is an integer
k ∈Q means k is a rational no.
k ∈R means k is a real no.
k ∈C means k is a complex no.
If you are interested in Set theory, you may read the book "Stories about Sets (集的故事)", it is a very good book to beginners.
At last, I would like to conclude with 2 question
i )Do the set N has less elements than that in I?
ii)Do the set I has less elements than that in Q?
The answer of this two questions can be found in the book mentioned above.
- kcLv 51 decade ago
May be you could have some ideas from the following web site:
- ipLv 71 decade ago
- 1 decade ago