On the Superstability Related with the Trigonometric Functional Equation.

We will investigate the superstability of the (hyperbolic) trigonometric functional equation from the following functional equations: f(x+y) ± g(x-y) = γf(x)g(y), f(x+y) ± g(x-y) = γg(x)f(y), f(x+y) ± g(x-y) = γf(x)f(y), f(x+y) ± g(x-y) = γg(x)g(y), which can be considered the mixed functional equations of the sine function and cosine function, of the hyperbolic sine function and hyperbolic cosine function, and of the exponential functions, respectively. [ABSTRACT FROM AUTHOR]