Solution of Hyers-Ulam stability problem for generalized Pappus' equation (Q1766719)

The authors generalize the famous Pappus' identity and introduce a new functional equation \[ n^2 f(x+my) + mnf(x-my) = (m+n)(nf(x) + mf(ny)) \tag \(*\) \] for given positive integers \(m\) and \(n\). By applying the direct method, they prove the Hyers-Ulam-Rassias stability of the equation (\(*\)) for a class of functions \(f : X \to Y\), where \(X\) is a vector space and \(Y\) is a Banach space.