Bhavin Mansukhlal Patel (2026) “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”, International Journal of Mathematics And its Applications, 13(4), pp. 41–53. Available at: https://ijmaa.in/index.php/ijmaa/article/view/1631 (Accessed: 9 January 2026).