1, positive number: a number greater than 0.

2. Negative number: a number less than 0.

3. Positive numbers are greater than 0, negative numbers are less than 0, and positive numbers are greater than negative numbers.

Note: 0 is neither positive nor negative; -a is not necessarily negative, and +a is not necessarily positive; P is not a rational number;

Second, rational numbers.

1, rational number: a number consisting of integers and fractions. Include positive integer, 0, negative integer, positive fraction and negative fraction. Can be written as the ratio of two integers. Irrational numbers cannot be written as the ratio of two integers. It is written in decimal form, and the numbers after the decimal point are infinite. Such as: π)

Third, count the axes.

1, number axis: Numbers are represented by points on a straight line, which is called number axis. Draw a straight line and take any point on the straight line to represent the number 0. This zero point is called the origin, which specifies that the right or upward direction of the straight line is positive; Select the appropriate length as the unit length, so as to take points on the number axis. )

2. Three elements of the number axis: origin, positive direction and unit length.

3. Antiquities: Only two numbers with different symbols are called reciprocal. The antonym of 0 is still 0.

Is the sum of opposites 0? a+b=0？ A and b are reciprocal.