释义 |
Logarithmic Spiral Evolute
 | (1) |
Using
 | (2) |
gives
and
so
and the Tangent Vector is given by
The coordinates of the Evolute are therefore
So the Evolute is another logarithmic spiral with , as first shown by Johann Bernoulli. However, in some cases, the Evolute is identical to the original, as can bedemonstrated by making the substitution to the new variable
 | (9) |
Then the above equations become
which are equivalent to the form of the original equation if
 | (12) |
 | (13) |
 | (14) |
where only solutions with the minus sign in exist. Solving gives the values summarized in the following table. |  |  | 1 | 0.2744106319... |  | 2 | 0.1642700512... |  | 3 | 0.1218322508... |  | 4 | 0.0984064967... |  | 5 | 0.0832810611... |  | 6 | 0.0725974881... |  | 7 | 0.0645958183... |  | 8 | 0.0583494073... |  | 9 | 0.0533203211... |  | 10 | 0.0491732529... |  |
ReferencesLauwerier, H. Fractals: Endlessly Repeated Geometric Figures. Princeton, NJ: Princeton University Press, pp. 60-64, 1991. |