Since 2 is in A, 2*2 = 4 must be in A. Since 4 and 2 are in A... can you take it from here?
I've been looking at this problem for ages and still can't work out what to do so help would be much appreciated!
Set A is defined recursively. Find four elements in Set A.
2 ∈ A
x, y ∈ A, then x*y ∈ A (multiplication)
[I thought a clause may have been missing, but not entirely sure.. recursion isn't a strong point of mine..]