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如何计算等差数列中的项数

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有时我们在数学中会遇到这样的问题，需要找出等差数列中的项数。这个问题并不难，按照以下方法就能求出。

步骤

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题目中可能会直接给出公差，或者在数列的首或尾给出两个连续的数字。公差用d表示。 ^{[1]
X
研究来源}
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要求出等差数列的项数必须要知道首项和末项。找出后记下来。首项用A表示，末项用L表示。 ^{[2]
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研究来源}
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3
用下列公式计算项数：项数用n表示。 公式为：
```
n = (L-A)/d + 1
```
公式很简单。用末项（L）与首项（A）之差除以公差（d），再加1。 ^{[3]
X
研究来源}
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小提示

末项与首项之差总是能被公差整除。

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警告

不要将首末项之差与公差混淆。

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