To determine which option demonstrates that polynomials form a closed system under multiplication, we need to ensure that when two polynomials are multiplied, the result is also a polynomial.
Let's analyze each option:
-
First option:
\[
5 \cdot 3x
\]
- This simplifies to \(15x\), which is a polynomial. This option demonstrates closure under multiplication.
-
Second option:
\[
(13)(x^4 - 2)
\]
- This simplifies to \(13x^4 - 26\), which is also a polynomial. This option demonstrates closure under multiplication.
-
Third option:
\[
5x^{-1} \cdot 2
\]
- Here, \(x^{-1}\) indicates that this term is not a polynomial (since it includes a negative exponent). Thus, the product \(10x^{-1}\) is not a polynomial. This option does not demonstrate closure under multiplication.
-
Fourth option:
\[
2x^3 + x^2
\]
- This is a polynomial expression, but it does not show multiplication of two polynomials. This option does not demonstrate closure under multiplication.
Conclusion
The first two options demonstrate that polynomials form a closed system under multiplication:
- \(5 \cdot 3x\)
- \((13)(x^4 - 2)\)
Both of these options confirm that the result after multiplying polynomials remains a polynomial.
If you need to select just one response that clearly shows this property, either the first option or the second option would be valid choices.