2007 AMC 8 第 16 题

先试着解答 2007 AMC 8 第 16 题,然后核对你的答案与精心整理的解答,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 2007 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。

16.

Amanda Reckonwith 画了五个半径为 11、22、33、44 和 55 的圆。然后对每个圆,她描点 (C,A)(C, A),其中 CC 是圆的周长,AA 是圆的面积。下列哪一个可能是她的图?
Amanda Reckonwith draws five circles with radii 1,1, 2,2, 3,3, 44 and 5.5. Then for each circle she plots the point (C,A),(C, A), where CC is its circumference and AA is its area. Which of the following could be her graph?
答案:A
知识点:圆面积圆周长二次方程
小提示:
用半径表示周长和面积
Write circumference and area in terms of the radius.
大提示:
当周长随半径线性增长时,面积随半径平方增长
As the circumference grows linearly with radius, the area grows quadratically.
解答:
半径 11 到 55 的圆的周长分别为 2π2\pi、4π4\pi、6π6\pi、8π8\pi 和 10π10\pi,对应面积分别为 π\pi、4π4\pi、9π9\pi、16π16\pi 和 25π25\pi。
当 CC 等量增加时,AA 增加得越来越快,所以这些点形成递增的二次形状。只有图 A 有这种形状。
所以正确答案是 A。
The circumferences of circles with radii 11 through 55 are 2π,2\pi, 4π,4\pi, 6π,6\pi, 8π,8\pi, and 10π10\pi. Their respective areas are π,\pi, 4π,4\pi, 9π,9\pi, 16π,16\pi, and 25π25\pi.
As CC increases by equal amounts, AA increases more and more quickly, so the points form an increasing quadratic pattern. Only graph A has that shape.
Thus, A is the correct answer.
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