Question

Which of these expressions is equivalent to z^8–1?

(z^4+1)(z^2–1)(z–1)(z–1)
(z^4–1)(z^2–1)(z–1)(z–1)
(z^4+1)(z^2+1)(z+1)(z–1)
(z^4+1)(z^2+1)(z–1)(z–1)

I Think it is either A or C, is one of these correct?

Answer 1

let a = z^4
(a^2-1) = (a-1)(a+1)
= (z^4-1)(z^4+1)

=(z^2-1)(z^2+1)(z^4+1)
=(z^4+1)(z^2+1)(z+1)(z-1)

Answer 2

not good