Factorise:

The given expression is $x^{2}+13 x+40$.

Find two numbers that follow the conditions given below:

Sum $=13$

Product $=40$

Clearly, the numbers are 8 and 5 .

$x^{2}+13 x+40=x^{2}+8 x+5 x+40$

$=x(x+8)+5(x+8)$

$=(x+8)(x+5)$