function err = bdf2(x0,h)
    % formule de differences finies BDF2
    diff = ????? ;
    err = abs(diff - df(x0));
    fprintf(' x0 = %e, h = %e, erreur = %e \n',x0,h,err)
end

% la fonction f
function funct = f(x)
    funct = ????? ;
end

% la derivee de f
function dfunct = df(x)
    dfunct = ????? ;
end
