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In this paper, by using fixed point theorem, we obtain the stability of the following functional equations \begin{align*} f(pr,qs)+g(ps,qr)&=\theta(p,q, r,s)f(p,q)h(r,s) \\ f(pr,qs)+g(ps,qr)&=\theta(p,q, r,s)g(p,q)h(r,s), \end{align*} where $G$ is a commutative semigroup, $\theta : G^{4} \rightarrow \mathbb{R}_{k}$ a function and $f,g,h$ are functionals on $G^{2}$.

In this paper, we present an extention of Hyers–Ulam stability of Sahoo–Riedel’s points for real-valued differentiable functions on [a, b] and then we obtain stability results of Flett’s points for functions in the class of continuously differentiable functions on [a, b] with f′(a) = f′(b).

In this article, we present generalized Hyers–Ulam stability results of a cubic functional equation associated with an approximate cubic Lie derivations on convex modular algebras χρ with Δ2-condition on the convex modular functional ρ.

In this paper, we solve the Hyers-Ulam stability problem for the following cubic type functional equation f(rx + sy) + f(rx− sy) = rsf(x + y) + rsf(x− y) + 2r(r − s)f(x) in quasi-Banach space and non-Archimedean space, where r 6= ±1, 0 and s are real numbers.

In this paper, we prove the generalized Hyers{Ulam stability of an n-dimensional additive functional equation, and then apply stability results to Banach modules over a unital Banach algebras.

In this paper, we consider the Hyers-Ulam stability of Cauchy type functional equations of module left (m,n)-derivations and generalized module left (m,n)-derivations in complete metric spaces.

In this paper, we give a general solution of a refined quadratic functional equation and then investigate its generalized Hyers-Ulam stability in quasi-normed spaces and in non-Archimedean normed spaces.