1、【2020新】北师大版六年级下册数学课件图形的放大和缩小课后课后作业作业探索探索新知新知1课堂探究点课堂探究点2课时流程课时流程课堂课堂小结小结当堂当堂检测检测你见过左面这些现象吗？你见过左面这些现象吗？这些现象中，哪些是把这些现象中，哪些是把物体放大？哪些是把物物体放大？哪些是把物体缩小？体缩小？探究点探究点 在方格纸上按一定比将图形放大或缩小在方格纸上按一定比将图形放大或缩小 “巨人巨人”的身高与普通人的身的身高与普通人的身 高的比是高的比是4:1。该如何为该如何为“巨人巨人”设计一间教室呢？设计一间教室呢？按相同的比放大按相同的比放大如果图中的长方形表示我们教室的大小，你能按如果图中的长
2、方形表示我们教室的大小，你能按4:1的比将图形放大，画出的比将图形放大，画出“巨人巨人”教室的大小吗？教室的大小吗？2464:11234:16243126243366312哪种设计更合理呢？哪种设计更合理呢？放大前后图形对应放大前后图形对应线段长的比相等。线段长的比相等。如果下图中的三角形表示巨人用的三角尺，你能将这个三角形如果下图中的三角形表示巨人用的三角尺，你能将这个三角形按按1:4缩小，画出我们用的三角尺吗？缩小，画出我们用的三角尺吗？88281:4281:422281:4缩小前后图形对应缩小前后图形对应线段长的比相等。线段长的比相等。小试牛刀小试牛刀（源于（源于典中点典中点）1填空。填
3、空。(1)一个长方形的长是一个长方形的长是24 cm，宽是，宽是18 cm，如果把它，如果把它按按1 3缩小，长变为缩小，长变为()cm，宽变为，宽变为()cm。(2)一个正方形的边长是一个正方形的边长是8 cm，将其按，将其按()放大后放大后的边长是的边长是24 cm。(3)一个圆按一个圆按3 1放大后，半径是放大后，半径是12 cm，原来圆的周，原来圆的周长是长是()cm。863 125.12(4)下图中下图中()号图形是号长方形放大后的图形，号图形是号长方形放大后的图形，它是按它是按()()放大的。图中放大的。图中()号图形号图形是号长方形缩小后的图形，它是按是号长方形缩小后的图形，它是
4、按()()缩小的。缩小的。1.51122把图形按把图形按3 1放大，把图形按放大，把图形按1 2缩小。缩小。归纳总结：归纳总结：（讲解源于（讲解源于典中点典中点）图形放大和缩小的特点：形状不变，大图形放大和缩小的特点：形状不变，大小改变。图形放大和缩小的方法：一看，小改变。图形放大和缩小的方法：一看，二算，三画。二算，三画。小试牛刀小试牛刀（教材（教材P25练一练）练一练）1.下面哪个图形是图下面哪个图形是图A按按2:1的比例放大后的图形？哪个图的比例放大后的图形？哪个图 形是图形是图A按按1:2缩小后的图形？缩小后的图形？图图E是图是图A按按2 1的比放大后的图形。的比放大后的图形。图图C是
5、图是图A按按1 2的比缩小后的图形。的比缩小后的图形。2.下面的每个方格表示下面的每个方格表示1cm2。先按要求将图形放大或缩小，。先按要求将图形放大或缩小，再回答问题。再回答问题。（1）将下面的正方形缩小，使缩小后的图形与原图形对）将下面的正方形缩小，使缩小后的图形与原图形对 应线段长的比为应线段长的比为1:3。想一想，缩小后的图形与原图形的面积比也是想一想，缩小后的图形与原图形的面积比也是1:3吗？吗？1:92.下面的每个方格表示下面的每个方格表示1cm2。先按要求将图形放大或缩小，。先按要求将图形放大或缩小，再回答问题。再回答问题。（2）将下面的长方形放大，使放大后的图形与原图形对）将下
6、面的长方形放大，使放大后的图形与原图形对 应线段长的比为应线段长的比为2:1。想一想，放大后的图形与原图形的面积比也是想一想，放大后的图形与原图形的面积比也是2:1吗？吗？4:13.找一找生活中有哪些把图形或物体按比例放大与缩小的找一找生活中有哪些把图形或物体按比例放大与缩小的 现象，与同伴交流。现象，与同伴交流。4.将下面的图形按比例放大或缩小，比一比谁画得像？将下面的图形按比例放大或缩小，比一比谁画得像？略。略。易错辨析易错辨析3把下面图形按把下面图形按1 2缩小后画在方格纸上。缩小后画在方格纸上。易错点：缩小要注意形状不能变，也就是角度不能变。易错点：缩小要注意形状不能变，也就是角度不能
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21、obtained from the person concerned and the relevant obligee.转载或引用本文内容必须是以新闻性或资料性公共免费信息为使用目地地合理、善意引用，不得对本文内容原意进行曲解、修改，并自负版权等法律责任.Reproduction or quotation of the content of this article must be reasonable and good-faith citation for the use of news or informative public free information.It shall not
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23、盈利性用途，但同时应遵守著作权法及其他相关法律地规定，不得侵犯本网站及相关权利人地合法权利.除此以外，将本文任何内容或服务用于其他用途时，须征得本人及相关权利人地书面许可，并支付报酬.Users may use the contents or services of this article for personal study,research or appreciation,and other non-commercial or non-profit purposes,but at the same time,they shall abide by the provisions of co
24、pyright law and other relevant laws,and shall not infringe upon the legitimate rights of this website and its relevant obligees.In addition,when any content or service of this article is used for other purposes,written permission and remuneration shall be obtained from the person concerned and the r
25、elevant obligee.转载或引用本文内容必须是以新闻性或资料性公共免费信息为使用目地地合理、善意引用，不得对本文内容原意进行曲解、修改，并自负版权等法律责任.Reproduction or quotation of the content of this article must be reasonable and good-faith citation for the use of news or informative public free information.It shall not misinterpret or modify the original intentio
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27、利.除此以外，将本文任何内容或服务用于其他用途时，须征得本人及相关权利人地书面许可，并支付报酬.Users may use the contents or services of this article for personal study,research or appreciation,and other non-commercial or non-profit purposes,but at the same time,they shall abide by the provisions of copyright law and other relevant laws,and shal
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29、用目地地合理、善意引用，不得对本文内容原意进行曲解、修改，并自负版权等法律责任.Reproduction or quotation of the content of this article must be reasonable and good-faith citation for the use of news or informative public free information.It shall not misinterpret or modify the original intention of the content of this article,and shall b
30、ear legal liability such as copyright.版权申明本文部分内容，包括文字、图片、以及设计等在网上搜集整理.版权为个人所有This article includes some parts,including text,pictures,and design.Copyright is personal ownership.用户可将本文地内容或服务用于个人学习、研究或欣赏，以及其他非商业性或非盈利性用途，但同时应遵守著作权法及其他相关法律地规定，不得侵犯本网站及相关权利人地合法权利.除此以外，将本文任何内容或服务用于其他用途时，须征得本人及相关权利人地书面许可，并支
31、付报酬.Users may use the contents or services of this article for personal study,research or appreciation,and other non-commercial or non-profit purposes,but at the same time,they shall abide by the provisions of copyright law and other relevant laws,and shall not infringe upon the legitimate rights of
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