Stability and nonstability of the radical Drygas type functional equation

Abstract

We introduce and find the general solution of the following radical Drygas type functional equation:

f((2I+1)root u(2l+1)+v(2l+1))+f((2l+1)root u(2l+1)-v(2l+1))=2f(u)+f(v)+f(-v)

for all u, v is an element of R, where l is a fixed positive integer. Also, we investigate the Hyers-Ulam stability via Brzdek's fixed point technique.