计算圆周直径
只要知道一个圆周的任一参数，计算其直径很容易：半径、周长、面积。如果你不知道以上数据，但是有圆周的图，也可以算出直径。假如你想知道如何计算圆周的直径，遵照以下步骤进行即可。
步骤
方法 1 的 2:
利用半径、周长或面积计算圆周直径
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1
假如你知道圆周的半径，它的两倍就是直径。半径是从圆周中心到边缘的距离。举例说明，如果圆周的半径是4厘米，那么圆周的直径就是4厘米x 2，也即8厘米。
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2
如果你知道圆周的周长，将其除以 π即可得到直径。Π值约为3.14，但你应该用计算器得到最精确的结果。举例说明，如果圆周周长是10厘米，那么直径就是10厘米/ π，也即3.18厘米。
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3
如果你知道圆周的面积，算出其平方根，再将结果除以π即可得到半径。这涉及到对圆周面积公式A = πr2进行转换，得出直径。举例说明，如果圆周面积为25平方厘米，求平方根则有√25平方厘米 = 5厘米。然后，将结果除以π。5厘米/π = 1.59厘米，因此圆周半径即为1.59厘米，其直径则为1.59厘米 x 2，也即3.18厘米。
方法 2 的 2:
通过圆周图计算直径
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1
在圆周内一侧圆弧到另一侧画一条水平线。用直尺或平直边缘来画。这条线可以在圆周上班不，也可靠近底部，或是在中间的任何位置。
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2
将直线与圆周相交的点标为“A”和“B”。
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3
分别以A和B为圆心画两个重叠的圆。确保两个圆像文氏图那样相互重叠。
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4
以一条垂直线连接圆周相交的两点。这条线就是圆周的的直径。
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5
测量直径。用直尺测量，或者为了增加精确性，用数显卡尺来测量。这样就大功告成了！
小提示
- 熟练使用圆规。这种工具用途广泛，包括如上所述作图得出圆周直径。分线规（与圆规类似）有时也可用于此类情形。
- 多加练习，使用几何公式与等式就会更加得心应手。向在圆规或其他几何形状上有经验的人请教。你很可能会发现有了经验之后，几何问题看起来就没那么困难了。
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