Consider the function f(x) = x on the interval [-π, π]. Which of the following is the Fourier series of f(x)?
1
\(\sum_{n=1}^{\infty} \frac{2}{n} \sin (nx) \)
2
\(\sum_{n=1}^{\infty} \frac{2}{n} \cos (nx) \)
3
\(\sum_{n=1}^{\infty} \frac{1}{n} \sin (nx) \)
4
\(\sum_{n=1}^{\infty} \frac{1}{n} \cos (nx) \)