2025 AMC 8 第 10 题

先试着解答 2025 AMC 8 第 10 题,然后核对你的答案与视频与精心整理的解答,解答来自 LIVE by Po-Shen Loh。你也可以参加完整限时模拟考试、查看全部 2025 AMC 8 解答,或核对答案。

所有题目均经美国数学协会(MAA)官方合法授权使用。

10.

下图中,ABCDABCD 是一个矩形,边长 AB=5AB = 5 英寸,AD=3AD = 3 英寸。矩形 ABCDABCD 顺时针旋转 90∘90^\circ,旋转中心是边 DCDC 的中点,得到第二个矩形。两个重叠矩形覆盖的总面积是多少平方英寸?
In the figure below, ABCDABCD is a rectangle with sides of length AB=5AB = 5 inches and AD=3AD = 3 inches. Rectangle ABCDABCD is rotated 90∘90^\circ clockwise around the midpoint of side DCDC to give a second rectangle. What is the total area, in square inches, covered by the two overlapping rectangles?
2121
22.2522.25
2323
23.7523.75
2525
答案:D
知识点:变换面积容斥原理
小提示:
把两个矩形面积相加,再减去重叠面积
Add the two rectangle areas and subtract the overlap
大提示:
重叠部分是一个边长为 55 英寸边一半的正方形
The overlap is a square whose side is half of the 55-inch side
视频讲解:
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文字解答:
最直接的方法是用容斥:把两个矩形的面积相加,再减去重叠的正方形面积。
每个矩形面积为 5×3=155 \times 3 = 15。
重叠部分是边长 2.52.5 的正方形,面积为 2.52=6.252.5^2 = 6.25。
因此总覆盖面积为 15+15−6.25=23.7515 + 15 - 6.25 = 23.75,选 D。
The easiest way to solve this problem is using the Inclusion-Exclusion formula. That is: add the areas of the two rectangles, and then subtract the overlapping (square) area.
Each rectangle has area 5×3=15.5 \times 3 = 15.
Their overlap is a square that has side length 2.5,2.5, and so its area is 2.52=6.25.2.5^2 = 6.25.
Therefore, the total area is 15+15−6.25=23.75,15 + 15 - 6.25 = 23.75, which is choice D.
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