Correct Answer - Option 2 : x - 2

**Given:**

Factor of the x3 + ax + b is,

(x - 1), and (x + 3)

**Calculation:**

**Let,**

(x - β) is the remaining factor of the given equation then,

⇒ (x - β)(x - 1)(x + 3) = x3 + ax + b

⇒ (x - β)[x^{2} + 2x - 3] = x3 + ax + b

⇒ x^{3} + 2x^{2} - 3x - βx^{2} - 2βx + 3β = x3 + ax + b

⇒ x^{3} + x^{2}(2 - β) - x(3 + 2β) + 3β = x3 + ax + b

**On comparing both side,**

⇒ 2 - β = 0

**β = 2**

Hence,** the remaining factor is (x - 2)**