syms n x pi
a0 = int(x^3 + 3, 0, 1)
an = int((x^3 + 3) * cos(n * pi * x), 0, 1)
f = sym(((1 / n^2) * ((-1)^n - 2 * (-1)^n / (pi^2 * n^2) + 2 / (pi^2 * n^2)) * cos(pi * n * x)) * cos(n * pi * x))
z5 = symsum(f, 'n', 1, 5) * (6 / (pi^2)) + 13/4
z10 = symsum(f, 'n', 1, 10) * (6 / (pi^2)) + 13/4
ezplot(z5, -10, 10)
hold on
ezplot(z10, -10, 10)