23.9. в) (n² + np + p²)(n - p);

Recognize the difference of cubes formula: a³ - b³ = (a - b)(a² + ab + b²).

1. In this case, a = n and b = p.
2. Therefore, (n² + np + p²)(n - p) = n³ - p³.

Answer: n³ - p³