plotting the step function including trigonometry expressions

Dear Maxima' s users,

I need to draw the graph of the functions such as

x (t ) = 1/4t sin 2t - u (t - 2pi  ) ? 1/4 (t - 2pi ) sin 2(t - 2pi )


In doing so, I used the following syntax to get the graph of the x(t)


plot2d(1/4*t*sin(2*t)-
unit_step(t-2*pi)*1/4*(t-2*pi)*sin(2*t-4*pi),[t,0,3*pi]);


but, I didn't get any graphs. I have the same problem for drawing the graph
of
y1:t+cos(t)-(sin(2*pi*t-1)+cos(t))*unit_step(t-2*pi);
and
y2:cos(2*t)-cos(2*t)*unit_step(t-2*pi);

May I have the appropriate syntax to get the graph of the functions?
Your apply is highly regarded,

Fereshteh,