Problem plot B1:

The function
       { -1  -Pi   < x < -Pi/3
g(x) = {  1  -Pi/3 < x <  Pi/3
       { -1   Pi/3 < x <  Pi
has fourier series
                     ( oo                      )
                     (----                     )
          1      4   ( \   sin(n Pi/3) cos n x )
g(x) = - ---  + ---- (  ) ---------------------)
          3      Pi  ( /           n           )
                     (----                     )
                     (n = 1                    )

Plot g and its best approx for N = 1, 2, 4, and 5 on the
same graph.