An approximation circuit approximates a function f of an input value x by adding at least the first two terms in a Taylor series and f) where a is a number reasonably close to value x. After several pre-treatment steps to modify the surface situation of the substrate, whether for metallic or plastic material, to enhance the adhesion of above coating layers, a layer of mirror finish will be applied, with the function of decoration shown with metal appearance and glossy. extend upwardly from centers of the triangle sides. Methods of making these compounds and their use for inhibiting the growth of S.