Question

Which of the following is equal to the following expression:
$x^2+13x+40$

• A. $(x+5)(x-8)$
• B. $(x+5)(x+8)$
• C. $(x-5)(x+8)$
• D. $(x-5)(x-8)$

Answer 1

The correct option is B $(x+5)(x+8)$

Using the identity:
$(x+a)(x+b)=x^2+(a+b)x+ab{x}^2+13x+40=x^2+(5+8)x+(5\times 8)(\because 8+5=13and8\times 5=40)\Rightarrow x^2+13x+40=(x+5)(x+8)$