By definition we have to:
A set has under an operation if performance of that operation on set members always produces a member of the same set; in this case we also say that the set is closed under the operation.
For this case we have the following polynomials:

Multiplying we have:

The product of two polynomials is also a polynomial.
Answer:
d
is a polynomial
Answer:
a = ±10/9
Step-by-step explanation:

Answer:
(0,-1)
Step-by-step explanation:
7. Obtuse
8. Acute
9. No, because it’s the hypotenuse
10. Yes, because that part is not the hypotenuse and it is less than the greatest angle