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)
x² + 10 x + 21 = ( x² + 3 x ) + ( 7 x + 21 )
= x ( x + 3 ) + 7 ( x + 3 ) = ( x + 3 ) ( x + 7 )
(x + 3)(x + 7)
(x + 4)(x + 6)
(x + 6)(x + 15)
(x + 7)(x + 14)
= x ( x + 3 ) + 7 ( x + 3 ) = ( x + 3 ) ( x + 7 )