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45 lines
781 B
Markdown
45 lines
781 B
Markdown
---
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id: 5900f4571000cf542c50ff6a
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title: '问题 235：算术几何序列'
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challengeType: 1
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forumTopicId: 301879
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dashedName: problem-235-an-arithmetic-geometric-sequence
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---
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# --description--
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Given is the arithmetic-geometric sequence $u(k) = (900 - 3k)r^{k - 1}$.
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Let $s(n) = \sum_{k=1 \ldots n} u(k)$.
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Find the value of $r$ for which $s(5000) = -600\\,000\\,000\\,000$.
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Give your answer rounded to 12 places behind the decimal point.
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# --hints--
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`arithmeticGeometricSequence()` should return `1.002322108633`.
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```js
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assert.strictEqual(arithmeticGeometricSequence(), 1.002322108633);
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```
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# --seed--
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## --seed-contents--
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```js
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function arithmeticGeometricSequence() {
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return true;
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}
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arithmeticGeometricSequence();
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```
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# --solutions--
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```js
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// solution required
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```
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