\(\begin{array}{l}\text { b) } x(x-9)+2 x-18=0 \\ x(x-9)+2(x-9)=0 \\ (x-9)(x+2)=0 \\ \Leftrightarrow x-9=0 \text { hay } x+2=0 \\ \Leftrightarrow x=9 \text { hay } x=-2\end{array}\)