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In geometry, a golden spiral is a logarithmic spiral whose growth factor is , the golden ratio.〔Chang, Yu-sung, "(Golden Spiral )", The Wolfram Demonstrations Project.〕 That is, a golden spiral gets wider (or further from its origin) by a factor of for every quarter turn it makes. ==Formula== The polar equation for a golden spiral is the same as for other logarithmic spirals, but with a special value of the growth factor : : or : with being the base of Natural Logarithms, being an arbitrary positive real constant, and such that when is a right angle (a quarter turn in either direction): : The numerical value of depends on whether the right angle is measured as 90 degrees or as radians; and since the angle can be in either direction, it is easiest to write the formula for the absolute value of (that is, can also be the negative of this value): : for in degrees; : for in radians . An alternate formula for a logarithmic and golden spiral is: : where the constant is given by: : which for the golden spiral gives values of: : if is measured in degrees, and : if is measured in radians. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「golden spiral」の詳細全文を読む スポンサード リンク
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