neya3311, hello
You never told us what you wanted us to do with these polynomials?!
Factor them perhaps?
x4 - 1 = (x2 + 1)(x + 1)(x - 1)
x3 - 11x2 + x - 11 = (x2 + 1)(x - 11)
Please let me know if this helps, I'm anxious to know what you were asking...