Найдите наибольший корень уравнения x4-4x3+6x2-4x+1=0

x^4-4x^3+6x^2-4x+1=0 x(x^3-4x^2+6x)=-1 x=-1 или  x^3-4x^2+6x=-1                   x(x^2-4x+6)=-1                    x=-1 или x^2-4x+6=-1                                     x^2-4x=-7                                     x(x-4)=-7                                     x=-7 или x-4=-7                                                      x=-3