推荐回答(1个)
从几何意义上讲,在给定线段AC上黄金均值可以这样构成,在AC上取一点B,使
则|AB|为黄金均值,也以黄金分割、黄金比以及黄金比例等著称.
一条线段一旦分割出黄金均值,那么黄金矩形也就很容易通过以下步骤作出:
1)给定任一线段AC,用B点将线段AC分割出一个黄金均值段,作正方形ABED.
2)作CF⊥AC.
3)延长射线DE,使得线DE与CF交于F点.
则ADFC是一个黄金矩形.
黄金矩形也可以不用已有的黄金均值段作出,如下图所示:
1)作任意正方形ABCD.
2)用线段MN将正方形平分为两半.
3)用圆规,以N为中心,以|CN|为半径作弧.
4)延长射线AB直至与以上的弧相交于E点.
5)延长射线DC.
6)作线段EF⊥AE,并令射线DC与EF交于F点.
则ADFE为一黄金矩形.
黄金矩形还能自我产生:从下面的黄金矩形ABCD出发,很容易通过画正方形ABEF的方法得到黄金矩形ECDF.再通过画正方形ECGH,容易构成黄金矩形DGHF.这样的过程可以无限地继续下去.
用最后得到的无穷多个紧挨着的黄金矩形,可以作出另一种类型的等角螺线(也称对数螺线).如下图用圆规在一系列黄金矩形中的各个正方形里,画四分之一圆弧.这些弧便形成等角螺线的轮廓.
注释
由黄金矩形陆续产生其他的黄金矩形,这样便画出了等角螺线的轮廓.图中的对角线交点为该螺线的极点或中心.
令O为螺线的中心.
螺线的极半径是指以中心O和螺线上任意点为端点的线段.
注意螺线上的每一个点的切线与该点的极半径都形成一个角∠T1P1O.如果对于每一个这样的角都相等,则该螺线为等角螺线.
等角螺线也称对数螺线,因为它以几何比率(也就是某数的方幂)增长,而方幂的指数则是对数的另一种名称.
等角螺线是仅有的这样一种类型的螺线,这种螺线当它增大时不改变自己的形状.
在实际生活中有许多装点的形式——正方形、六角形、圆、三角形等等.黄金矩形和等角螺线是其中最令人心旷神怡的两种.两者的形迹可见于海星、贝壳、菊石、鹦鹉螺、序状种子的排列、松果、菠萝、甚至于一个蛋的形状.
同样令人感兴趣的是黄金比与斐波那契数列的联系.斐波那契数列——(1,1,2,3,5,8,13,…,[Fn-1+Fn-2],…)——相继项
除了出现在艺术、建筑和自然界外,今天黄金矩形还在广告和商业等方面派上用场.许多包装采用黄金矩形的形状,能够更加迎合公众的审美观点.例如标准的信用卡就近似于一个黄金矩形.
黄金矩形还跟许多其他的数学观念相联系.诸如无穷数列、代数、圆内接正十边形、柏拉图体、等角螺线、极限、黄金三角形和五角星形等等.
参考资料:http://ced.xxjy.cn/RESOURCE/CZ/CZSX/SXBL/SXTS1059/5146_SR.HTM
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