function t = ch5(n, x)
% ch5 - calculate T_n(x) using recurrence relations
%       T_n+1(x) = 2*x*T_n(x) - T_n-1(x) 
    tm = x .^ 0;
    tn = x;
    for i = 1:n-1
        tp = 2 .* x .* tn - tm;
        tm = tn;
        tn = tp;
    end
    t = tp;
end