Introduction to Functional equations and Ulam stability theory.- Stability and instability of multiplicative inverse type tredecic and quottuordecic functional equations in non-Archimedean spaces.- Estimation of inexact multiplicative inverse type quindecic and sexdecic functional equations in Felbin's type fuzzy normed spaces.- Classical approximations of multiplicative inverse type septendecic and octadecic functional equations in quasi-β-normed...