hi. i need to find the roots of $\displaystyle 2x^3+5$ over the complexs, reals, and rationals. i don't know what to do other than trial and error.. i am starting with the complex. exactly the roots should be easy to find. but i am trying an online calculator and it is telling me the cube root of -5/2 has no real root.. this is not true.. so i am confused. i also don't understand how a polynomial with odd degree can have a complex root.. if someone can help me please give me a pointer for this. then thank you. what i don't understand is that with the odd degree, the imaginary part will not disappear as it is supposed to.