Plastic Number
Plastic number may refer to: * Plastic ratio, a mathematical ratio * Resin identification code The Resin Identification Code (RIC) is a technical standard with a set of symbols appearing on plastic products that identify the Synthetic resin, plastic resin out of which the product is made. It was developed in 1988 by the Society of the P ...

Plastic Ratio
In mathematics, the plastic ratio is a geometrical aspect ratio, proportion, given by the unique real polynomial root, solution of the equation Its decimal expansion begins as . The adjective ''plastic'' does not refer to Plastic, the artificial material, but to the formative and sculptural qualities of this ratio, as in ''plastic arts''. Definition Three quantities are in the plastic ratio if \frac =\frac =\frac The ratio is commonly denoted Substituting b=\rho c \, and a=\rho b =\rho^2 c \, in the middle fraction, \rho =\frac. It follows that the plastic ratio is the unique real solution of the cubic equation \rho^3 -\rho -1 =0. Solving with Cubic equation#Cardano's formula, Cardano's formula, \begin w_ &=\frac12 \left( 1 \pm \frac13 \sqrt \right) \\ \rho &=\sqrt[3] +\sqrt[3] \end or, using the Cubic equation#Trigonometric and hyperbolic solutions, hyperbolic cosine, :\rho =\frac \cosh \left( \frac \operatorname \left( \frac \right) \right). is the superstabl ...
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