if f( x ) = x^5 - 2x^3 + x^2 + 2
and you are looking for x where f( x ) = - 1, than it is the same if you write:
x^5 - 2x^3 + x^2 + 2 = - 1 , and that is equal to:
x^5 - 2x^3 + x^2 + 3 = 0 , so solution of this equation is the answer to your question... ( solution can be from R or from C )