% x2 freqentiel

N = 20;
fe = 50*N*f0;
Tps = [0 :1/fe: 1-1/fe];
for r = [1/2,1/3,1/4]
    a0 = r;
    x = a0 * ones(1,length(Tps));
    for n = 1:N
        an = 2*sin(n*pi*r)/(n*pi);
        x = x + a0 + an*cos(n*2*pi*f0*Tps);
    end
    X=fft(x);
    Frq = [0 : fe/length(x) : fe - fe/length(x)];
    figure
    plot(Frq,abs(X));
    xlabel = "f";
    ylabel = "Sx2(f)";
    Title = "DSP de x2";
end