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Second, choose

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Third, the judge.

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This part of the extended materials mainly examines the knowledge points of the least common multiple:

The common multiple of two or more integers is their common multiple, and the smallest common multiple except 0 is called the smallest common multiple of these integers. The least common multiple of integers a and b is marked as [a, b]. Similarly, the least common multiples of a, b and c are marked as [a, b, c], and the least common multiples of multiple integers also have the same marks.

The concept corresponding to the least common multiple is the greatest common divisor, and the greatest common divisor of A and B is denoted as (a, b). Regarding the least common multiple and the greatest common divisor, we have the following theorems: (a, b) x [a, b] = ab (both a and b are integers).

The least common multiple of natural numbers A and B can be written as [a, b], and the greatest common factor of natural numbers A and B can be written as (a, b). When (a, b)= 1, [a, b] = a× B. If two numbers are multiples, their least common multiple is a larger number, and the least common multiple of two adjacent natural numbers is their product. The least common multiple = the product of two numbers/the maximum agreed (cause) number, and confusion with the maximum agreed (cause) number problem should be avoided when solving the problem.

The scope of application of the least common multiple: addition and subtraction of fractions, China's remainder theorem (the correct problem has a solution and a unique solution within the least common multiple). Because prime numbers are numbers that cannot be divisible by numbers other than 1 and their own numbers; The n power of prime number X can only be divisible by the n power and the lower power of X, 1 and its own number. Therefore, a definition of the least common multiple is given: the least common multiple of the number S is the product of the highest power of the prime factor contained in this number S.