Charlie subtracts two polynomials, 2x^2 -2x^2, and says that the difference proves that polynomials are not closed subtraction. Kate argues that the difference does in fact show that polynomials are closed under subtraction. Who is correct? Charlie or Kate.

Kate is correct.

The difference of 2x^2 - 2x^2 results in 0, which is still a polynomial. This demonstrates that polynomials are closed under subtraction, as the result of the subtraction is still a polynomial.