found the solution. these will create 3 iepitations.
%%1
N = 10000;
t = linspace(-pi, pi, N + 1)'; t(end) = [];
x = -t;
t1 = linspace(-3*pi, 3*pi, 3*N)';
X=[x;x;x];
figure; hold on; grid on;
plot(t1, X, 'b', 'LineWidth', 1)
legend('x(t)', 'y(t)');
xlabel('t');
ylabel('x(t)');