From my understanding,
In the problem stated above the dimension of
2*cos(t) is 1×11 double
2*sin(t) is 1×11 double
So, the third argument passing to the function should be of 1×11 double size.
You can use something like below
t=0:pi/10:pi
plot3(2*cos(t),2*sin(t),t) % t is 1×11 double size