What is the difference of the polynomials? open paren x to the 4th power plus x cubed plus x squared plus x close paren minus open paren x to the 4th power minus x cubed plus x squared minus x close paren

Distribute the subtraction across the second polynomial, changing each of its signs: (x⁴ + x³ + x² + x) − (x⁴ − x³ + x² − x) = x⁴ + x³ + x² + x − x⁴ + x³ − x² + x. The x⁴ and x² terms cancel, leaving 2x³ + 2x. This matches choice D.

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