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.
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.
LCM of 21 & 49 is 147, so all multiples of 147 are common multiples of 21 & 49.
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