1. Addition, subtraction, multiplication and division are easy to verify. Just use (m 1+n 1* radical number 2) and (m2+n2* radical number 2) to verify.

So I will focus on the organization. The denominator of division can't be 0, and 0 is obviously ∈A, so I don't think the division operation is closed, but if this situation is excluded, that is, the denominator =0, it can still be proved to be closed. . .

So I said I'm not sure.

I think this topic is about domain.

a-b={y|y=x^2,x>； 3 or x

B-A={x|x∈ and x 2 ≠ y}

These two sets intersect and then write them together.

a△B = { y | x & gt； 3 or x

Hehe, I don't know right or wrong, just do it ~ ~