问题 填空题

把一个圆分成若干(偶数)等份,拼成一个近似的长方形,这个长方形的长是圆的______,宽是圆的______,所以圆的面积公式是S=______.

答案

因为近似长方形的长等于圆周长的一半,宽等于圆的半径.

圆的面积=近似长方形的面积,

=长×宽,

=πr×r,

=πr2

所以把一个圆分成若干等份.然后剪开拼成一个近似的长方形,这个长方形的长相当于圆的周长的一半,长方形的宽就是圆的半径.因为长方形的面积=长×宽,所以圆的面积=πr2

故答案为:周长的一半,半径,πr2

材料分析题

为积极响应全市“从我做起,走向文明”主题实践活动,某校七年级(2)班学生利用周六到附近福利院进行卫生大扫除活动。赵明放学回家同妈妈说起此事时,妈妈把脸一沉,立即反对说:“作为学生好好学习就行了,万一摔着你怎么办,那些活留给你同学干吧。” 面对这种情景,假若你是赵明,你会去做?

                                                                                                                                                               

                                                                                                                                                               

                                                                                                                                                               

                                                                                                                                                                

                                                                                                                                                              

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