I am trying to evalute symbolically a matrix looking like this:

V := (Matrix(3, 3, [[0, 0, 0], [0, 0, 0], [0, 0, 0]]) - (((1/2) . (Vector[row](3, [0, 0, 0]))) . (Matrix(3, 3, [[0, 0, 0], [0, 0, 0], [0, 0, 0]])))) . (Vector[column](3, [0, 0, 0]))

Here is the picture because the formatting is bad:

I need to have some equations in this form but maple wont allow me.

Let us say there is a function desribing an angle. And by deriving the math let us say the position is cos(theta). Theta is a function of time and cos is a function. How do i differentiate this and make maple see that theta is a function and not a variable.

i have tried this (x(t) is theta):

f := t -> sin(x(t));
Diff(f, t);

Did not work.What i want is the output to be.

cos(x(t))*x'(t)