Thay \(x\) bởi \(\dfrac{1}{x}\) ta được: \(f\left(\dfrac{1}{x}\right)+2f\left(x\right)=\dfrac{1}{x}\)
Ta có hệ \(\left\{{}\begin{matrix}f\left(x\right)+2f\left(\dfrac{1}{x}\right)=x\\f\left(\dfrac{1}{x}\right)+2f\left(x\right)=\dfrac{1}{x}\end{matrix}\right.\)