Question 16****+For which integers \(k\) with \(0\le k\le7\) is \(e^{2\pi ik/8}\) a primitive eighth root of unity?
Question 18*****A learner lists \(e^{2\pi ik/5}\) for every integer \(k\) as infinitely many fifth roots of unity. Explain the mistake.
Question 20*****Show that the product of two \(n\)-th roots of unity is again an \(n\)-th root of unity.