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”. International Journal of Mathematics And its Applications 13, no. 4 (January 1, 2026): 41–53. Accessed January 9, 2026. https://ijmaa.in/index.php/ijmaa/article/view/1631.