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In the last four decades, the orthogonal functions approach has been extensively applied to study problems like analysis, identification, and control of continuous-time dynamical systems. The success of this approach lies in the fact that it converts calculus into algebra approximately in the sense of least squares. Sine-cosine functions are a class of orthogonal functions, and they were applied to study the optimal control problem with some success. In order to have a computationally attractive method for solving the optimal control problem via sine-cosine functions, an attempt was made. In this note, we show that the Fourier series approach to the optimal control problem in a paper by Endow (Optimal control via Fourier series of operational matrix of integration, IEEE Trans. Autom. Control, vol. 34, no. 7, p. 770-3, Jul. 1989) is incorrect.