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Question
If n is any positive integer, write the value of \[\frac{i^{4n + 1} - i^{4n - 1}}{2}\].
Solution
\[\frac{i^{4n + 1} - i^{4n - 1}}{2}\]
\[ = \frac{i - \frac{1}{i}}{2} \left( \because i^{4n} = 1, i^{- 1} = \frac{1}{i} \right)\]
\[ = \frac{\frac{i^2 - 1}{i}}{2}\]
\[ = \frac{i^2 - 1}{2i}\]
\[ = \frac{- 1 - 1}{2i}\]
\[ = \frac{- 2}{- 2i} \]
\[ = \frac{- 1}{i}\]
\[ = \frac{- i}{i^2} \left( \because i^2 = - 1 \right)\]
\[ = \frac{- i}{- 1}\]
\[ = i\]
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