How do you factor completely x^6-1x61?

1 Answer
May 13, 2016

(x-1)(x+1)(x^2-x+1)(x^2+x+1)(x1)(x+1)(x2x+1)(x2+x+1)
=(x-1)(x+1)(x-1/2-i sqrt3/2)(x-1/2+i sqrt3/2)(x+1/2-i sqrt3/2)(x+1/2+ i sqrt3/2)=(x1)(x+1)(x12i32)(x12+i32)(x+12i32)(x+12+i32)

Explanation:

The answer in the given form can be obtained directly by observing that it is a cubic in x^2x2.

x^6-1=(x^2)^3-1^3x61=(x2)313

=(x^2-1)((x^2)^2+x^2+!)=(x21)((x2)2+x2+!)

=(x-1)(x+1)(x^4+x^2+1)=(x1)(x+1)(x4+x2+1)

=(x-1)(x+1)(x^2-x+1)(x^2-x+1)=(x1)(x+1)(x2x+1)(x2x+1)

=(x-1)(x+1)(x-1/2-i sqrt3/2)(x-1/2+i sqrt3/2)=(x1)(x+1)(x12i32)(x12+i32)

(x+1/2-i sqrt3/2)(x+1/2+ isqrt3/2)(x+12i32)(x+12+i32)

The expanded form can be directly obtained from

(x^6-1)=prod(x-e^(i(2kpi)/6))(x61)=(xei2kπ6), k=0, 1, 2,..,5.,

using the six 6th roots of 1, {e^(i(2kpi)/6)}{ei2kπ6}, k=0, 1, 2,..,5.,