Johnchau123,
If I understand your question correctly, S1 is not a function of x. Its summation is 1.64493406684822643637 according to the CRC Standard Mathematical Tables.
Actually what I mean is as there are sine and cosine function of x in the series.
So, I would like to ask what value of x should be used so that some terms eliminate, say, if i would like to evaluate Σ(-1)^n/(n^2), what I should do is to substitute 2pi into the first series with range pi < x < 3pi.
Hi, everyone, I get the solution of this question.
I put x = 1 into the Fourier series which is available for 1 < x < 2. As the Fourier series is continuous on (1,2) and its derivative is also continuous on (1,2), so, we apply the mean value theorem and can find at x = 1, x² = 5/2 and the sum of this series is pi²/6.