Which expression is the factorization of x^2 + 10x + 21?

(x+3) (x+7)

(x + 3) (x + 7).

Step-by-step explanation:

x^2 + 10x + 21.

You need 2 numbers whose product is the last number in the function (+21) and whose sum is the coefficient of x (+10).

These are + 3 and + 7, so the factors are:

(x + 3) (x + 7).