初三数学,关于圆

2024-12-01 09:51:38
推荐回答(3个)
回答1:

帮你搜了个答案

答:可以切割出66个小正方形.(1分)

方法一:

(1)我们把10个小正方形排成一排,看成一个长条形的矩形,这个矩形刚好能放入直径为10.05cm的圆内,如图中矩形ABCD.

∵AB=10BC=10.

∴对角线AC平方=100+1=101<10.05平方.(3分)

(2)我们在矩形ABCD的上方和下方可以分别放入9个小正方形.

∵新加入的两排小正方形连同ABCD的一部分可看成矩形EFGH,矩形EFGH的长为9,高为3,对角线EG^2=9^2+3^2=81+9=90<10.05^2.但是新加入的这两排小正方形不能是每排10个,因为:

10^22+3^2=100+9=109>10.052.(6分)

(3)同理:8^2+5^2=64+25=89<10.05^2,

9^2+5^2=81+25=106>10.05^2,

∴可以在矩形EFGH的上面和下面分别再排下8个小正方形,那么现在小正方形已有了5层.(8分)

(4)再在原来的基础上,上下再加一层,共7层,新矩形的高可以看成是7,那么新加入的这两排,每排都可以是7个但不能是8个.

∵7^2+7^2=49+49=98<10.05^2,

8^2+7^2=64+49=113>10.05^2.(9分)

(5)在7层的基础上,上下再加入一层,新矩形的高可以看成是9,这两层,每排可以是4个但不能是5个.

∵4^2+9^2=16+81=97<10.05^2,

5^2+9^2=25+81=106>10.05^2,

现在总共排了9层,高度达到了9,上下各剩下约0.5cm的空间,因为矩形ABCD的位置不能调整,

故再也放不下一个小正方形了.

∴10+2×9+2×8+2×7+2×4=66(个).(10分)

方法二:

学生也可能按下面的方法排列,只要说理清楚,评分标准参考方法一.

可以按9个正方形排成一排,叠4层,先放入圆内,

然后:(1)上下再加一层,每层8个,现在共有6层;

(2)在前面的基础上,上下各加6个,现在共有8层;

(3)最后上下还可加一层,但每层只能是一个,共10层.

这样共有:4×9+2×8+2×6+2×1=66(个).

 

 

回答2:

老天呀,怎么什么问题都有呀!

回答3:

1矩形的四个顶点在同一圆上
正确圆心为矩形两对角线交点
2菱形四条边的中点在同一个圆上
正确
菱形四边中点连线为矩形,则同1
3等腰梯形的四个顶点在同一个圆上
正确
等腰梯形两斜边的中垂线交点为圆心
4直角三角形的三个顶点在以斜边中点为圆心的同一个圆上
正确
直角三角形斜边中点到三顶点距离相等,则此点为圆心

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