23.9. б) (a + x)(a² + ax + x²);

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

1. The given expression is (a + x)(a² + ax + x²). This does not directly match the sum of cubes formula.
2. Let's expand it: (a + x)(a² + ax + x²) = a(a² + ax + x²) + x(a² + ax + x²)
3. = a³ + a²x + ax² + a²x + ax² + x³
4. = a³ + 2a²x + 2ax² + x³

Answer: a³ + 2a²x + 2ax² + x³