18, 36, 54, 72, 90, 108.
First three common multiples of 2 and 6 are 6, 12 and 18.
The first three common multiples are 18, 36, and 54.
The first five multiples of 6 are 6, 12, 18, 24 and 30. For them to be common, they need to be compared to another set of multiples.
3: 3, 6, 9, ... 6: 6, 12, 18, ... 18: 18, 36, 54, ... The lcm(3, 6, 18) = 18, so the multiples of 18 are common multiples of all of them.
The common multiples of 6 and 9 are the infinite set of multiples of their LCM, which is 18. So the common multiples of 6 and 9 are 18, 36, 54, 72, 90, 108, 126, 144, 162, 180, and so on.
They are: 6, 12 and 18
6, 12 and 18
6, 12, 18
6, 12, 18, 24
6, 12, 18
18, 36, 54
Multiples of 6 include 6, 12 and 18. For them to be common, they need to be compared to another set of multiples.