On the rational number in the first unit of the first volume of mathematics of the first grade of junior high school,

On the rational number in the first unit of the first volume of mathematics of the first grade of junior high school,

Fill in the blanks
1. The introduction of negative numbers is a practical need. We use positive numbers to express quantities with opposite meanings. For quantities with opposite meanings, we can define one of them as a positive number, and the quantity with opposite meanings is a negative number
2. If the water level drops by 3 meters, it is recorded as - 3 meters. If the water level rises by 4 meters, it is recorded as + 4
3. If an instrument rotates 45 ° clockwise, it is recorded as - 45 °, then 120 ° means 120 ° counterclockwise
4. A student's scores in three examinations are 57, 78 and 90, and 60 is considered as passing. Please use positive and negative numbers to indicate that the student's passing score is - 3 + 18 + 30
5. Going south - 20 meters means going north 20 meters
6. If the income is a positive number, the actual income of expenditure - 130 yuan is 130 yuan
8. Only two numbers with different symbols are called opposite numbers. The opposite number of 0 is 0
10. If two numbers are opposite to each other, the sum of them is 0
11. If a = - 4, then - a = 4; if - x = 3.1, then x = - 3.1
12. The absolute value of - 5 is 5, the absolute value of 10.1 is 10.1, the absolute value of 0 is 0, the absolute value of 3 is - 3 or + 3, and the absolute values of 12 and - 12 are equal
13. The number axis is a straight line that defines the origin, positive direction and unit length. On the number axis - 3 is on the left side of the origin and - 2.5 is on the right side of - 3
14. The number represented by two unit length points on the number axis is positive and negative 2
15. The opposite of a is____ -a___ If the opposite of a number is the smallest positive integer, then the number is____ -1____ .
16. The rational number with the smallest absolute value is_____ 0_____ An integer whose absolute value is less than 3 is____ 0、1、2_____ .
17. Negative integers with absolute values greater than 1 and less than 5 have______________ -2、-3、-4_____________ .
18、_____ 1______ The absolute value of is equal to the absolute value of its reciprocal
19. Given that 2a and 3-A are opposite to each other, then a=_____ 1______ .
20. If a and B are opposite to each other and C and D are reciprocal to each other, then A-CD + B=__ -1__ ,3a+4cd+3b=__ +4__