On positive answer to El-Fassi’s question related to hyperstability of the general radical quintic functional equation in quasi-β-Banach spaces.

In this paper, we are interested to study El-Fassi’s question on hyperstability of the general radical quintic functional equation in quasi- β -Banach spaces in [6]. First, we give some counterexamples to show that the hyperstability of a given functional equation does not occur. Then, by using the (β , p) -normalization theorem, we prove the stability for the general radical quintic functional equation in quasi- β -Banach spaces. [ABSTRACT FROM AUTHOR]