2026年一本周末小测卷七年级数学上册苏科版第21页答案
24. 新考法 规律探究(10分)《庄子》一书中记载:“一尺之棰,日取其半,万世不竭.”其大意是:一尺长的木棍,每天截掉一半,永远也截不完.古人在两千多年前就有了数学极限思想,今天我们运用此数学思想研究下列问题.
(1)规律探索:如图1,正方形的边长为1,将它沿虚线剪掉一半,则$S_{阴影1}=1-\frac{1}{2}=\frac{1}{2}$;
如图2,在图1的基础上,将阴影部分再沿虚线剪掉一半,则$S_{阴影2}=1-\frac{1}{2}-(\frac{1}{2})^2=(\frac{1}{2})^2=\frac{1}{4}$;
依此类推,
如图3,$S_{阴影3}=1-\frac{1}{2}-(\frac{1}{2})^2-(\frac{1}{2})^3=\_\_\_\_\_\_$;
如图4,$S_{阴影4}=1-\frac{1}{2}-(\frac{1}{2})^2-(\frac{1}{2})^3-(\frac{1}{2})^4=\_\_\_\_\_\_$;
……
$S_{阴影n}=1-\frac{1}{2}-(\frac{1}{2})^2-(\frac{1}{2})^3-\dots-(\frac{1}{2})^n=\_\_\_\_\_\_$.

(2)规律应用:计算$\frac{1}{2}+(\frac{1}{2})^2+(\frac{1}{2})^3+\dots+(\frac{1}{2})^{10}$的值.

答案

24. 解:(1)$S_{阴影3}=1-\frac{1}{2}-(\frac{1}{2})^2-(\frac{1}{2})^3=(\frac{1}{2})^3=\frac{1}{8}$;
$S_{阴影4}=1-\frac{1}{2}-(\frac{1}{2})^2-(\frac{1}{2})^3-(\frac{1}{2})^4=(\frac{1}{2})^4=\frac{1}{16}$;
$S_{阴影n}=1-\frac{1}{2}-(\frac{1}{2})^2-(\frac{1}{2})^3-\dots-(\frac{1}{2})^n=(\frac{1}{2})^n=\frac{1}{2^n}$.
故答案为$\frac{1}{8},\frac{1}{16},\frac{1}{2^n}$.
(2)因为$1-\frac{1}{2}-(\frac{1}{2})^2-(\frac{1}{2})^3-\dots-(\frac{1}{2})^{10}=\frac{1}{2^{10}}$,所以$\frac{1}{2}+(\frac{1}{2})^2+(\frac{1}{2})^3+\dots+(\frac{1}{2})^{10}=1-\frac{1}{2^{10}}$.
解题大招
利用数形结合,将算式转化为计算图形的面积,从而解决问题.