polynomial equation

This may help

http://en.wikipedia.org/wiki/Nth_root

a much more rigorous work can be found here:

http://www-history.mcs.st-and.ac.uk/HistTopics/Fund_theorem_of_algebra.html

applying simple logic that polynomial of degree two has two roots similarly polynomial of n degree has n no; of roots use brain it will simple crack iit

She needed proof. So we gave her links for that. By the way, they might also be given in some elementary text books.