how did Cardano obtain three solutions for cubic? So, if I am not mistaken Complex numbers were discovered after Cardano's method. But from Cardano's Method on Wikipedia, it says to get the three solutions, we should use the root of unity. In that case, when Cardano's method was published it could only find one solution?  

For example, to find the cube roots of unity, take the solutions of the equation $$x^3=1,$$ which can be found by writing $$x^3-1=0\longrightarrow(x-1)(x^2+x+1)=0.$$
Cardano's method produces a similar result for a certain class of cubic equations. 
The root of $x-1$ of course is real but the others are nonreal conjugates.
