arbitrary symbolic functions - Symbolic math toolbox

I have an equation:

M = A sin(x(t));

and would like to find: dM/dt

is it possible to create symbolic functions without definition? for x(t) I dont have a definition. But I require:

diff(M,t).

How can an arbitrary symbolic function be declared??

Answer 1

[Walter Roberson]

A = 9/13;   %arbitrary
syms x(t)
M = A * sin(x(t));
diff(M,t)

[Maria Perdomo]

syms x(t) ??? Error using ==> syms at 61 Not a valid variable name.

I can declare symbolic variables but cannot declare symbolic functions. why could this be?

[Walter Roberson]

You must have an older version of MATLAB.

[Maria Perdomo]

2010b. I'll try a newer version. Thanks!

[Maria Perdomo]

yep it is, 2012a works.