One, enumeration method (enumerating all the factors of two numbers, and then finding out that the same factor is the common factor of two numbers)

For example, find the common factor of 18 and 24.

Factors of 18: 1, 2, 3, 6, 9, 18.

Factors of 24: 1, 2, 3, 4, 6, 8, 12, 24.

So the common factor of 18 and 24 is 1, 2, 3, 6.

Second, first find out the factors of the smaller number, and then find out which are the factors of another number, so which numbers are the common factors of two numbers.

For example, the factors of 18: 1, 2, 3, 6, 9, 18.

In 1, 2,3,6,9, 18, 1, 2,3,6 is a factor of 24.

So the common factor of 18 and 24 is 1, 2, 3, 6.

Three, decomposition of prime factor method (not commonly used, but must be mastered)

For example: 18=2×3×3.

24=2×2×2×3

The factorization prime factors of 18 and 24 both have factors 2 and 3.

At the same time, there are 2×3 and 2×3=6.

In natural numbers, the smallest factor of any number is 1.

So to sum up, the common factor of 18 and 24 is 1, 2, 3, 6.