Geometry people answer this im struggling or at least tell me how to solve it

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

In the xy-plane, if the parabola with equation passes through the point (-1, -1), which of the following must be true?

1- what do you think the product of a nonzero rational number and an irrational number is? is it rational or irrational? make use of variables, the closure property of integers, and possibly a proof by contradiction to prove your hypothesis.2- why do we have to specify that the rational number must be nonzero when we determine what the product of a nonzero rational number and an irrational number is? if the rational number were 0, would it give us the same result we found in the first question?