Solution and stability of generalized mixed type cubic, quadratic and additive functional equation in quasi-Banach spaces

In this paper, we achieve the general solution and the generalized Hyers–Ulam–Rassias stability of the following functional equation f(x+ky)+f(x−ky)=k2f(x+y)+k2f(x−y)+2(1−k2)f(x)f(x+ky)+f(x−ky)=k2f(x+y)+k2f(x−y)+2(1−k2)f(x) for fixed integers kk with k≠0,±1k≠0,±1 in the quasi-Banach spaces.