Question: Which of the following is the factorization of x² + 10x + 21?

Options:

1. (x + 3)(x + 7)
2. (x + 1)(x + 21)
3. (x + 2)(x + 10)
4. (x + 5)(x + 5)

Correct Answer: (x + 3)(x + 7)

Solution:

x² + 10x + 21 = (x + 3)(x + 7) because 3 and 7 add to 10 and multiply to 21.