Question 344326
Complex solutions always come in complex conjugate pairs. 
So, if {{{3i}}} is a solution, then {{{-3i}}} is also a solution. 

{{{(x-3i)(x+3i)=x^2+9}}}
You can then use polynomial long division to find the last root, 
You can then get {{{(x^3-2x^2+9x-18)/(x^2+9)}}}
Also, since only one root remains you know it must be real. 
You could graph the equation and find it that way too.
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{{{graph(300,300,-10,10,-10,10,x^3-2x^2+9x-18)}}}
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Looks like {{{x=2}}} might be a number to stick in the function to see if {{{f(2)=0}}}.