Notice that:
[tex]\begin{gathered} -18=(-9)\cdot2, \\ -9+2=-7. \end{gathered}[/tex]
Therefore:
[tex](x-9)(x+2)=x^2-7x-18.[/tex]
If x²-7x-18=0 then:
[tex]\begin{gathered} x-9=0\text{ or x+2=0,} \\ x=9\text{ or x=-2.} \end{gathered}[/tex]
Answer: x=9 or x= -2.
