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我们知道,圆的面积计算公式是S=πr~2。根据公式可知,要求圆的面积,应先知道它的半径是多少。那么,求圆的面积是不是一定要先知道它的半径呢?一、知道r~2可以直接求圆的面积【例】(如图)阴影部分面积是10平方厘米,求圆的面积。因为阴影部分是个正方形,它的边长正好是圆的半径r,它的面积正好是r~2。根据公式可以直接将r~2的值与π相乘,就求出了圆的面积。即:3.14×10=31.4(平方厘米)。
We know that the area of a circle is calculated as S = πr ~ 2. According to the formula we can see that the required area of the circle, you should first know how much its radius. So, seeking the area of the circle is not necessarily the first to know its radius? First, we know that r ~ 2 can directly find the area of the circle [Example] (Figure) shaded area is 10 square centimeters, seeking round area. Since the shaded part is a square, its length is exactly the radius r of the circle, and its area is exactly r2. According to the formula can be directly r ~ 2 multiplied by the value of π, to find the circle area. That is: 3.14 × 10 = 31.4 (square centimeters).