  In this paper, we achieve the general solution and the generalized
  Hyers-Ulam-Rassias stability of the following functional equation
$$f(x+ky)+f(x-ky)=k^2f(x+y)+k^2f(x-y)+2(1-k^2)f(x)\eqno {2 cm}$$for fixed
integers $k$ with $k\neq0,\pm1$ in the quasi-Banach spaces.
