Factor the expression.?

x^2 + 10x + 21
= x^2 + 3x + 7x + 21
= (x^2 + 3x) + (7x + 21)
= x(x + 3) + 7(x + 3)
= (x + 3)(x + 7)

x^2 + 10x + 21 = (x+7)(x+3) answer//

x^2 + 10x + 21 = x2 + 7x + 3x + 21
. . . . . . . . . . . = x(x + 7) + 3(x + 7)
. . . . . . . . . . . = (x + 3)(x + 7) ....................... Answer

(x+7)(x+3) = 0

(x+7)(x+3)
because 3 times 7 is 21 and 3 plus 7 is ten

x² + 10x + 21 = (x + 3)(x + 7)