They are: 63, 126, 189, 252, 315, 378.
21, 42 and 63
They are: 21, 42 and 63
If that's 9, 14 and 21, the first three common multiples are 126, 252 and 378.
LCM of 21 & 49 is 147, so all multiples of 147 are common multiples of 21 & 49.
The multiples of 3 are 3, 6, 9, 12, 15, 18, 21 and so on. The first six multiples of 6 are 6, 12, 18, 24, 30, 36, 42 and so on. Common multiples include all the multiples of 6.
105 and 210
21
42 63 84 105 126 147
there are infinite amount of common multiples.
The common multiples of 9 and 21 are 63, 126, 189 and so on.
Two common multiples of 21 and 15 are 105 and 315.
7, 14, 21