The sum of digits of (1) product is 9; (For example, 3927, 2+7 = 9; ……)
② The tenth digit of the product is always smaller than the first digit in the formula1; (For example: 6954, five is 1 less than six; ……)
(3) Starting from "Nine from Nine", the number of digits in the next sentence increases by 1, and the number of digits decreases by1; Decimal digits went up from 1 to 9, and one digit went down from 9 to 1.
Multiplication formula of 9:
Nine-tenths, 298,3927,4936,59415,6954,79613,8972,9981.
Extended data:
Other multiplication formulas:
16 got 6,262,368,4624,5630,6636.
17 is 7,274,3721,4728,5735,6742,7749.
18 has 8,286,3824,48312,5840,68418,78516,8864.
China used the "99 formula" earlier. Sentences such as "3927", "684 18", "483 12" and "6636" can be found in books such as Xunzi, Guanzi, Huainanzi and Warring States Policy. It can be seen that as early as the Spring and Autumn Period and the Warring States Period, 99 multiplication songs became popular.
Jiujiubiao, also known as Jiujiuge and Jiuyinge, is the basic calculation rule in multiplication, division, square root and other operations in ancient China. It has been used for more than two thousand years. Pupils and some school-age children can recite it. But Europe didn't know this simple multiplication table until the beginning of 13 century.
The ancient western civilizations Greece and Babylon also invented the multiplication table, but it is more complicated than the 999 table. There are more than 1700 Greek multiplication tables invented by Babylon, and they are not complete enough. Because they worked hard to calculate multiplication and division before 13 century, people who can divide large numbers will be considered as experts in mathematics.
/kloc-At the beginning of the third century, the eastern calculation method was introduced to Europe through Arabs, and Europeans discovered its convenience, so they learned this new method. At that time, the topic of multiplying two numbers by a new method was the textbook of the university at that time.