Answer:
(x + 3)(x + 7)
Step-by-step explanation:
Given
x² + 10x + 21
Consider the factors of the constant term (+ 21) which sum to give the coefficient of the x- term (+ 10)
The factors are + 3 and + 7, since
3 × 7 = 21 and 3 + 7 = 10, hence
x² + 10x + 21 = (x + 3)(x + 7)
