7 A geometric series has second term 375 and fifth term 81.
- Show that the common ratio of the series is 0.6 .
- Find the first term of the series.
- Find the sum to infinity of the series.
- The \(n\)th term of the series is \(u _ { n }\). Find the value of \(\sum _ { n = 6 } ^ { \infty } u _ { n }\).
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