do you need the answer from the quadratic formula? if so:
[tex]\frac{b+/- \sqrt{-b^2-4(a)(c)} }{2(a)} [/tex]
x^2=a
-3x=b
-18=c
[tex]\frac{3+/- \sqrt{3^2-4(1)(-18)} }{2(1)}[/tex]
[tex]\frac{3+/- \sqrt{9+72} }{2}[/tex]
[tex]\frac{3+/- \sqrt{81} }{2}[/tex]
[tex]\frac{3+/- 9 }{2}[/tex]
[tex] \frac{3+9}{2}= \frac{12}{2} =6[/tex]
[tex] \frac{3-9}{2} = \frac{-6}{2} =-3[/tex]
Your answer would then be 6 and -3