+,-,X only
Yes, because there is no way of multiplying two polynomials to get something that isn't a polynomial.
None.
Division of one polynomial by another one.
they have variable
+,-,X only
It means that you can do any of those operations, and again get a number from the set - in this case, a polynomial. Note that if you divide a polynomial by another polynomial, you will NOT always get a polynomial, so the set of polynomials is not closed under division.
In my opinion the question is poorly defined, since "non-polynomial" could be just about anything.
Polynomials are the simplest class of mathematical expressions. The expression is constructed from variables and constants, using only the operations of addition, subtraction, multiplication and non-negative integer exponents.
Yes, because there is no way of multiplying two polynomials to get something that isn't a polynomial.
"Non-polynomials" may be just about anything; how alike or different they are will depend on what specific restrictions you put on such functions, or whether you are even talking about functions.
Other polynomials of the same, or lower, order.
None.
Addition and multiplication.
Addition, subtraction and multiplication.
Division of one polynomial by another one.
Yes.