The area of triangle in the encyclopedia of mathematical concepts in primary schools = base × height ÷2. Formula S= a×h÷2 square area = side length× side length formula S= a×a rectangular area = length× width formula S= a×b parallelogram area = bottom× height formula S= a×h trapezoid area = (upper bottom+lower bottom) × height ÷2 formula s = (a+b) cuboid volume. Volume = bottom area × height formula: V = volume of AAA cube = side length × side length × side length formula: V = perimeter of V = aaa circle = diameter × π formula: L = π d = area of 2π r circle = radius× radius× π. Formula: S = CH = π DH = 2π RH Surface area of a cylinder: The surface area of a cylinder is equal to the perimeter of the bottom multiplied by the height plus the area of the circles at both ends. Formula: S=ch+2s=ch+2πr2 Volume of cylinder: The volume of cylinder is equal to the bottom area multiplied by the height. Formula: V = V = volume of SH cone = 1/3 bottom × product height. Formula: V= 1/3Sh Fraction addition and subtraction: use denominator to add and subtract fractions, only add and subtract numerators, and the denominator remains unchanged. Fractions of different denominators are added and subtracted, first divided, then added and subtracted. The multiplication of fractions is: use the product of molecules as numerator and the product of denominator as denominator. The law of division of fractions: dividing by a number is equal to multiplying the reciprocal of this number. For reading and understanding, the following definition will be applied: formula 1. Arithmetic 1, additive commutative law: Two numbers are added to exchange the position of the addend, and the sum is unchanged. 2. Law of additive combination: 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. 3. Multiplication and exchange law: when two numbers are multiplied, the position of the exchange factor remains unchanged. 4. Multiplication and association law: When three numbers are multiplied, the first two numbers are multiplied, or the last two numbers are multiplied first and then the third number, and their products are unchanged. 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. Such as: (2+4) × 5 = 2 × 5+4 × 56. The essence 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. O is divided by any number that is not O. Simple multiplication: the multiplicand and the end of the multiplier are multiplied by O. You can multiply 1 before o first, and zero does not participate in the operation, and add a few zeros at the end of the product. 7. What is an 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. Basic properties of the equation: When both sides of the equation are multiplied (or divided) by the same number at the same time, the equation is still valid. 8. What is an equation? A: Equations with unknowns are called equations. 9. What is a linear equation with one variable? A: An equation with an unknown number of degree 1 is called a linear equation with one variable. Example method and calculation of learning linear equation of one variable. That is, an example is given to illustrate that the formula is replaced by χ and calculated. 10, fraction: divide the unit "1" into several parts on average, and the number representing such a part or points is called a fraction. 1 1, addition and subtraction of fractions: addition and subtraction of fractions with denominator, only numerator addition and subtraction, denominator unchanged. Fractions of different denominators are added and subtracted, first divided, then added and subtracted. 12. Comparison of fractional sizes: Compared with the denominator, the numerator is large and the numerator is small. Compare the scores of different denominators, divide them first and then compare them; If the numerator is the same, the denominator is big and small. 13, the fraction is multiplied by the integer, and the product of the multiplication of the fraction and the integer is the numerator, 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, the fraction divided by an integer (except 0) is equal to the fraction multiplied by the reciprocal of this 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 fraction: write the false fraction as an integer, and the true fraction is called with fraction. 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, the number A divided by the number B (except 0) is equal to the reciprocal of the number A multiplied by the number B. The formula of quantity relationship is 1, unit price× quantity = total price 2, single output× quantity = total output 3, speed× time = distance 4, work efficiency× time = total work 5, Complement+complement = and one addend = and+The other addend is the minuend-Mei Mei = differential Mei Mei May = differential factor × factor = product of one factor = product ÷ dividend of another factor = dividend ÷ quotient dividend = quotient × Example: 90 ÷ 5 ÷. 1 km = 1 km = 1 00m6543300 cm2 1 cm2 = 1000 mm2 1 m3 =10000. 5438+0000g = 1 kg = 1 kg 1 hectare = 10000 m2. 1 mu = 666.666 square meters. 1 l = 1 cubic decimeter = 1000 ml 1 ml = 1 cubic centimeter 7. What is the ratio? The division of two numbers is called the ratio of two numbers. For example, the first and second terms of the ratio of 2÷5 or 3:6 or 1/3 are multiplied or divided by the same number at the same time (except 0), and the ratio remains unchanged. 8. What is proportion? Two formulas with equal ratios are called proportions. For example, 3: 6 = 9: 18 9. The basic property of proportion: in proportion, the product of two external terms is equal to the product of two internal terms. 10, solution ratio: the unknown term in the ratio is called the solution ratio. For example, 3: χ = 9:1811,and the ratio: two related quantities, one of which changes and the other changes. If the ratio (i.e. quotient k) corresponding to these two quantities is constant, these two quantities are called proportional quantities, and the relationship between them is called proportional relationship. For example: y/x=k( k must be) or kx=y 12, inverse ratio: two related quantities, one of which changes and the other changes. If the product of two corresponding numbers in these two quantities is certain, these two quantities are called inverse proportional quantities, and their relationship is called inverse proportional relationship. For example: x×y = k( k must be) or k/x = y percentage: a number indicating that one number is a percentage of another number is called a percentage. Percentages are also called percentages or percentages. 13. To convert decimals into percentages, just move the decimal point to the right by two places and add hundreds of semicolons. In fact, to convert a decimal into a percentage, just multiply this decimal by 100%. To convert percentages to decimals, simply remove the percent sign and move the decimal point two places to the left. 14. When a fraction is converted into a percentage, it is generally converted into a decimal (except for the inexhaustible, three decimal places are generally reserved), and then the decimal is converted into a percentage. In fact, to turn a fraction into a percentage, you must first turn the fraction into a decimal and then multiply it by 100%. Divide the percentage into components, and rewrite the percentage into components first, so that the quotation that can be lowered can be made into the simplest score. 15, learn decimal component numbers and fractions to decimals. 16, greatest common divisor: several numbers can be divisible by the same number at the same time, and this number is called the greatest common divisor of these numbers. (or the common divisor of several numbers is called the common divisor of these numbers. The largest one is called the greatest common divisor. ) 17, prime number: the common divisor has only 1 two numbers, which is called a prime number. 18, least common multiple: the multiple shared by several numbers is called the common multiple of these numbers, and the smallest is called the least common multiple of these numbers. 19. Comprehensive score: dividing the scores of different denominators by the scores of the same denominator equals the original score, which is called comprehensive score. (Generally, the least common multiple is used) 20. Approximation: it is called reduction to change a fraction into a fraction equal to it, but with smaller numerator and denominator. (Use the greatest common divisor) 2 1. Simplest fraction: A fraction whose numerator and denominator are prime numbers is called simplest fraction. At the end of the score calculation, the score must be converted into the simplest score. Numbers in units of 0, 2, 4, 6 and 8 can all be divisible by 2, that is, they can be subtracted by 2. A number with a bit of 0 or 5 can be divisible by 5, that is, it can be subtracted by 5. Pay attention to the use of contracts. 22. Even and odd numbers: Numbers divisible by 2 are called even numbers. Numbers that are not divisible by 2 are called odd numbers. 23. Prime number (prime number): If a number only has 1 and its two divisors, it is called a prime number (or prime number). 24. Composite number: a number. If there are other divisors besides 1 and itself, such numbers are called composite numbers. 1 is neither prime nor composite. 28. Interest = principal × interest rate × time (time is usually in years or months, which should correspond to the unit of interest rate) 29. Interest rate: The ratio of interest to principal is called interest rate. The ratio of interest to principal for one year is called annual interest rate. The ratio of interest to principal in January is called monthly interest rate. 30. Natural number: An integer used to represent the number of objects is called a natural number. 0 is also a natural number. 3 1, Cyclic Decimal: a decimal, starting from a certain digit in the decimal part, and one or several numbers appear repeatedly in turn. Such decimals are called cyclic decimals. Like 3. 14 14 14 32, acyclic decimal: a decimal, starting from the decimal part, without one or several digits repeating in turn. Such a decimal is called acyclic decimal. Like 3. 14 1592654 33. Infinite acyclic decimal: a decimal, from the decimal part to the infinite digits, is called infinite acyclic decimal. For example, 3. 14 1592654...34. What is algebra? Algebra is to replace numbers with letters. 35. What is algebraic expression? Expressions expressed in letters are called algebraic expressions. Example: 3x =(a+b )*c