Which of the following responses shows that polynomials form a closed system under multiplication?

(1 point)

(x) (6x • -3)
3х^2/4-1
(х) (1/2х)
1/4x^3 •5

1 answer

To determine which of the provided responses demonstrates that polynomials form a closed system under multiplication, we need to ensure that multiplying any two polynomials results in a polynomial.

  1. (x)(6x • -3): This is an expression involving multiplication of polynomials:

    • The term \(6x, \cdot, -3\) is a polynomial (specifically, \(-18x\)), and multiplying it by another polynomial (the variable \(x\)) gives \(-18x^2\), which is also a polynomial.
  2. 3х^2/4 - 1: This expression contains a polynomial \(3x^2/4\) and a constant \(-1\), but it is not presented in a multiplicative context, so it doesn't demonstrate closure under multiplication.

  3. (х)(1/2х): In this case, you're multiplying two polynomials:

    • \(x\) is a polynomial, and \(1/2x\) is also a polynomial (specifically, it can be viewed as \( \frac{1}{2}x^1\)).
    • Their product is \((1/2)x^2\), which is a polynomial.
  4. 1/4x^3 • 5: This multiplication involves \(1/4x^3\) (a polynomial) multiplied by \(5\) (also considered a polynomial as it can be seen as \(5x^0\)). The product is \((1/4 \cdot 5)x^3 = \frac{5}{4}x^3\), which is a polynomial.

Based on these evaluations, the responses that clearly show closure under multiplication of polynomials are:

  • (x)(6x • -3)
  • (х)(1/2х)
  • 1/4x^3 • 5

Each of these involves multiplying polynomials to yield another polynomial. The expression 3х^2/4 - 1 does not represent a multiplication operation. Therefore, all three multiplicative expressions (1, 3, and 4) demonstrate that polynomials form a closed system under multiplication.