I have an assignment quesiton :

" let A_i be a subset of the reals and i is element of I = (1,...,n)

now let A = UNION (i is element of I) A_i

show that sup(A) = sup_iEI(sup(A))"

I hope that is understandable...

so taking the limit of both sides I have limA = lim U A_i, I'm not sure what the limit of the union of a set is. Am I on the right track?