A number set is a * * * set of numbers. Some commonly used number sets in mathematics and their notation: the * * composed of all non-negative integers in a number set is called a non-negative integer set (or natural number set) and recorded as n;

* * * of all positive integers except zero is called positive integer set, and it is recorded as N* or N+(“+ ("+"(marked with "+"in the lower right corner);

The * * * composed of all integers is called the integer set, which is denoted as z;

The * * * composed of all rational numbers is called rational number set, and it is recorded as q;

A * * * composed of all real numbers is called a real number set, which is denoted as r 。

The * * * of all imaginary numbers is called the imaginary number set, and it is recorded as c:

There are irrational number sets and so on.

A point set is the * * * value of a point. You should know that a point is represented by (x, y). Many points are put together to form a point set. For example, {(2,4), (10, -5), (0,0), (3,4)} means (2,4), (). Ask close questions

"* * *: Take certain objects as a whole and form a * * *." How to understand the "fixed object" in this sentence?

Determination: There is only one answer to whether some objects are elements of this * * * *, and they must not be ambiguous.

Can you understand it this way? "People whose height exceeds 1 .75m", "Teachers of Class 0 and Class 7" and "People younger than Chow Yun Fat" are all "confirmation".

And "big cantaloupe" and "heavy stone" are "uncertain".