On the Superstability of the Pexider Type Trigonometric Functional Equation

Abstract

We will investigate the superstability of the (hyperbolic) trigonometric functional equation from the following functional equations: f(x+y)±g(x−y)=λf(x)g(y) andf(x+y)±g(x−y)=λg(x)f(y), which can be considered the mixed functional equations of the sine function and cosine function, the hyperbolic sine function and hyperbolic cosine function, and the exponential functions, respectively.