WASET
    Soon-Mo Jung,  Hyers-Ulam Stability of Functional Equationf(3x) = 4f(3x − 3) + f(3x − 6).   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    February 2010, vol. 38(2). 292 - 295
    [viewed 28 March 2024]. Available from: https://publications.waset.org/pdf/13478.