(c)
$a_{1}a_{2}\ldots a_{n} = b_{n}\left( \frac{a_{1}a_{2}\ldots a_{n}}{b_{n}} \right)$
$= a_{n}b_{n}\left( \frac{a_{1}a_{2}\ldots a_{n - 1}}{b_{n}} \right)$
$= \left\lbrack (x)^{\frac{1}{2^{n - 1}}} - (y)^{\frac{1}{2^{n - 1}}} \right\rbrack\left( \frac{a_{1}a_{2}\ldots a_{n - 1}}{b_{n}} \right)$
$= b_{n - 1} \bullet a_{n - 1}\left( \frac{a_{1}a_{2}\ldots a_{n - 2}}{b_{n}} \right) = ... = \frac{x - y}{b_{n}}$