Factorise.

x² + 9x + 18

On comparing with standard quadratic equation that is

we have,

a = 1, b = 9 and c = 18

Now here,

Product ac = 118 = 18

Factors of 18; 29 and 63

Sum should be b = + 9

From above factors (+ 6x + 3x)

will give + 9x sum

therefore + 9x is replaced by ( + 6x + 3x)

Now above eq. becomes

x² + 6x + 3x + 18

⇒ ; taking x common

⇒ (x + 3)(x + 6)