| Exam Board | Edexcel |
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| Module | Paper 2 (Paper 2) |
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| Session | Specimen |
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| Topic | Geometric Sequences and Series |
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10. In a geometric series the common ratio is \(r\) and sum to \(n\) terms is \(S _ { n }\)
Given
$$S _ { \infty } = \frac { 8 } { 7 } \times S _ { 6 }$$
show that \(r = \pm \frac { 1 } { \sqrt { k } }\), where \(k\) is an integer to be found.