| Exam Board | OCR |
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| Module | Further Pure Core 2 (Further Pure Core 2) |
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| Session | Specimen |
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| Topic | Complex numbers 2 |
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10 Let \(C = \sum _ { r = 0 } ^ { 20 } \binom { 20 } { r } \cos r \theta\). Show that \(C = 2 ^ { 20 } \cos ^ { 20 } \left( \frac { 1 } { 2 } \theta \right) \cos 10 \theta\).