Main Question or Discussion Point
what is a singlet under SU(3)?
You might want to look up Young tableaux, which are very useful for computing products of irreps for unitary groups. They are a pictorial way of keeping track of the symmetries of irreducible tensor representations. Alternatively, there are various places to find tables of products.Okay, that explains a singlet. Thanks.
But what I still cant get is how we know that it is 1 + 8. For example i need to find what 3 x 3 x 3 is. How can I do that?