I should factorize following polynomial: P(x)=x^2n + 2cos(naπ)x^n + 1 in ℝ if i know that a is irrational number. Things that confuse me here are following: 1. When factorizing polynomials, i have known exponents (unlike here, where i have 2n and n) so i don't know what to do with them? 2. Why does it makes a difference if a is irrational number?