Question

左图中的圆半径为 $1$ 个单位。圆和内接正方形之间的区域被涂阴影。右图中的圆里，圆和内接正方形之间区域的四分之一被涂阴影。两圆中的阴影区域面积相同。右图圆的半径 $R$ 是多少？

The circle shown below on the left has a radius of $1$ unit. The region between the circle and the inscribed square is shaded. In the circle shown on the right, one quarter of the region between the circle and the inscribed square is shaded. The shaded regions in the two circles have the same area. What is the radius $R,$ in units, of the circle on the right?

$\sqrt{2}$

$2$

$2\sqrt{2}$

$4$

$4\sqrt{2}$

答案：B

知识点：相似长度、面积与体积的缩放关系

难度评级：1310

视频讲解：

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文字解答：

右图与左图相似，但右图的对应面积是左图的 $4$ 倍。

因此右图的每个长度都是左图相应长度的倍，所以 $R = 2$ 。正确答案是 B。 $R^2 = 4 \cdot 1^2,$

Only one quarter of the gap between the circle and square is shaded on the right. For that shaded area to equal the whole gap on the left, the entire gap on the right must have $4$ times the area of the gap on the left.

The two circle-and-square figures are similar, and their areas scale as the square of their radii. Thus $R^2 = 4 \cdot 1^2,$ so $R = 2,$ which is choice B.

2025 AMC 8 第 18 题

答案：B

难度评级：1310

视频讲解：

文字解答：

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