17. (a) Show that $x^n - 1 = (x - 1)(x^{n-1} + x^{n-2} + x^{n-3} + \dots + x^2 + x + 1)$. (b) Hence prove that: (i) $7^n - 1$ is divisible by 6 $\forall n \in \mathbb{Z}^+$,
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The formula for the sum of a geometric series is given by: S = a(1 - r^n) / (1 - r), where a is the first term, r is the common ratio, and n is the number of terms. Show more…
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