Bhavin Mansukhlal Patel. On the Stability of the Quadratic Functional Equation $f(2x+y) + f(x+2y)$ $= 4f(x+y) + f(x) + f(y)$ in $2$-Banach Space. Int. J. Math. And Appl. [Internet]. 2026 Jan. 1 [cited 2026 Jan. 9];13(4):41-53. Available from: https://ijmaa.in/index.php/ijmaa/article/view/1631