Take into account that for a polynomial function, the possible roots are given by the following quotient:
roots = p/q
where p is the constant of the function (and its factors) and q is the coefficient of the term with the greates degree (variable with greatest exponent) or its factors.
Then, based on the previous explanation, you have:
p = -9
q = 5
factors -9: -1, 1, -3, 3, -9, 9
factors 5: -1, 1, -5, 5
Hence, the possible factors are:
±1, ±3, ±9, ±1/5, ±3/5, ±9/5
and the roots:
roots = {i(√15)/5 , -i(√15)/5, √3, -√3}
The roots can be also obtained by using quadratic formula for x^2, and then, by applying square root to the result to obtain x.
