2. Three elements of the number axis: origin, positive direction and unit length.
3. To draw several axes:
(1) Draw a horizontal straight line, and take any point on this straight line to represent 0, which we call the origin o;
(2) On this straight line, the direction from the origin to the right is defined as the positive direction (indicated by the arrow), and the direction to the left is defined as the negative direction;
(3) Take an appropriate length (such as 1㎝) as the unit length, take a point from the origin to the right every unit length, indicating 1, 2, 3 ... in turn, take a point from the origin to the left every unit length, indicating-1, -2. ...
4. Function: Both rational numbers and irrational numbers can be represented by points on the number axis; On the contrary, any point on the number axis represents a rational number or an irrational number.
The number axis is a very important mathematical tool. Through it, the corresponding relationship between numbers and points on the number axis is established, and the internal relationship between numbers and points is revealed. It is the basis of "combination of numbers and shapes". The number axis is a practical tool for junior high school mathematics. The number axis of the first-year students paves the way for the following rectangular coordinate system, and many problems can be solved in the rectangular coordinate system. Of course, you can also use the number axis to understand the concepts of absolute value and reciprocal. The moving point problem on the number axis is also the first contact with the moving point problem in junior high school, which has never been encountered in primary school and is one of the key and difficult problems in junior high school.