In 1-2 sentences, explain why the following operation is a closed system under subtraction.

The operation is a closed system under subtraction because subtracting two polynomials of the same degree results in another polynomial of the same degree. Specifically, subtracting \( (2x^2 + 12x + 11) \) from \( (9x^2 + 17x + 13) \) yields a polynomial \( (7x^2 + 5x + 2) \), which retains the polynomial form.