Which expression is the factorization of x2 + 10x + 21?

(x + 3) (x + 7)

(x + 4) (x + 6)

(x + 6) (x + 15)

(x + 7) (x + 14)

The answer is (x + 3) (x + 7). x^2 + 10x + 21 = x^2 + 3x + 7x + 21 = (x^2 + 3x) + (7x + 21) = (x * x + 3 * x) + (7 * x + 7 * 3) = x * (x + 3) + 7 * (x + 3) = (x + 3) * (x + 7) = (x + 3) (x + 7). Therefore, the factorization of x^2 + 10x + 21 is (x + 3) (x + 7).

(x + 3) (x + 7) (x + 4) (x + 6) (x + 6) (x + 15) (x + 7) (x + 14)