You basically have to use the quadratic formula to solve this since there are no factors of - 9 which add to give 6.
[tex]x = \frac{ - b + - \sqrt{ {b}^{2} - 4ac} }{2a} [/tex]
Then you use
[tex]a {x}^{2} + bx + \: c[/tex]
To find which numbers will go into what place inside the quadratic equation.
So a = 1 (because x is alone)
b = 6
c = -9
Then you solve it. I've included a picture of how I did it and I got the answer x=-3+-3sqrt2