For the linear congruence equation , the general solution is given by where is a particular solution and and .

My book says for this general solution it forms 'd congruence classes mod n'. What does that mean?

I interpreted it as this:

is always a constant since so for some integer constant .

So which can be written as which says ' congruence classes mod '

There are congruence classes because so there are possible remainders, so there are congruence classes since there are possible remainders.

How did they get 'd congruence classes mod n'?