It is not true. You can "see" quite easily that 9x2 = 3x6 = 18.
Here's the trick to find the least common multiple:
Factorize both numbers:
9 = 3 x 3
6 = 3 x 2
Now for each factor, take the case of the most occurrances.
For 3 it is two times in 9, so we take 3x3
For 2 it is once in 5, so we take 2
Multiply these:
3x3x2 = 18, the least common multiple.
Another example: LCM(30, 45)
30 = 2 × 3 × 5
45 = 3 × 3 × 5
2 x 3x3 x 5 = 90
