Assuming f(x)=0
A method that can be used is so called "Magic Numers" ( My teacher algebra teacher ikes to call it)
First, find two factors that multiply to 18 and add to 11.
9 and 2
Set it in factor form
[tex](x + 9)(x + 2)[/tex]
[tex](x + 9)(x + 2) = 0[/tex]
So this means...
[tex]x + 9 = 0[/tex]
Or
[tex]x + 2 = 0[/tex]
Solve.
X can either be equal to -9 or -2
Hope this was clear :)