2. The law of addition and association: When three numbers are added, the first two numbers are added first, or the last two numbers are added first, and then the third number is added, and the sum remains unchanged. a+b+c=a+(b+c)。
3. Multiplicative commutative law: When two numbers are multiplied, the position of the commutative factor and the product remains unchanged. A× B = B× A。
4. Multiplication and association law: When three numbers are multiplied, the first two numbers are multiplied, or the second two numbers are multiplied first, and then the third number is multiplied, and the product remains unchanged. A× B× C = (A× B )× C。
5. Multiplication and distribution law: When two numbers are multiplied by the same number, you can multiply the two addends by this number respectively, and then add the two products, and the result remains unchanged. For example, (2+4)×5=2×5+4×5.
6. Nature of division: In division, the dividend and divisor are expanded (or reduced) by the same multiple at the same time, and the quotient remains unchanged. Divide 0 by any number that is not 0 to get 0.
7. Equation: An equation in which the value on the left of the equal sign is equal to the value on the right of the equal sign is called an equation. The basic property of the equation is that both sides of the equation are multiplied (or divided) by the same number at the same time, and the equation still holds.
8. Equations: Equations with unknowns are called equations.
9. One-dimensional linear equation: An equation with an unknown number and an unknown number is called a one-dimensional linear equation. N-n unknowns; Unknown supreme power
10. Score: divide the unit "1" into several parts on average, and the number representing such a part or score is called a score. 1 1. Law of addition, subtraction, multiplication and division of fractions;
Add and subtract fractions with the same denominator, only add and subtract numerators, and the denominator remains the same.
Fractions of different denominators are added and subtracted, first divided, then added and subtracted.
Multiplication of fractions: use the product of molecules as numerator and the product of denominator as denominator.
Division of fractions: dividing by a number is equal to multiplying the reciprocal of this number.
12. Score comparison: Compared with the denominator score, divide the scores of different denominators first and then compare them; If the numerator is the same, the denominator is big and small.
13. Fractions are multiplied by integers, and the numerator is the product of the multiplication of fractions and integers, and the denominator remains unchanged.
14. Fractions are multiplied by fractions, the product of numerator multiplication is numerator, and the product of denominator multiplication is denominator.
15. Fraction divided by integer (except 0) equals fraction multiplied by the reciprocal of the integer.
16. True fraction: The fraction with numerator less than denominator is called true fraction.
17. False fraction: the fraction with numerator greater than denominator or numerator equal to denominator is called false fraction. False score is greater than or equal to 1.
18. With score: write a false score as an integer and a true score, which is called with score.
19. The basic nature of the fraction: the numerator and denominator of the fraction are multiplied or divided by the same number at the same time (except 0), and the size of the fraction remains unchanged.
20. A number divided by a fraction is equal to the number multiplied by the reciprocal of the fraction.
2 1.A divided by b (except 0) equals the reciprocal of a multiplied by b.