Which expression is the factorization of x squared plus 10 x plus 21 ?

To factor x² + 10x + 21, find two numbers whose product is 21 and whose sum is 10. The numbers 3 and 7 meet both conditions, so x² + 10x + 21 = (x + 3)(x + 7). The correct choice is (x + 3) times (x + 7).

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