How to Specify Symbolic Variable Using Symbolic Toolbox

I have just downloaded the Symbolic Toolbox.

I am trying to specify the variable

theta_1

as a symbolic variable.

Omega(3,3) = (zeros) % Initialization 
sym(theta_1)         % Symbology Variable

% Omega Population
Omega(1,1) = 1
Omega(2,2) = cos(theta_1)
Omega(2,3) = sin(theta_1)
Omega(3,2) = -sin(theta_1)
Omega(3,3) = cos(theta_1)

In the command window I get a return that

"Undefined function or variable 'theta_1'.

How do I define theta_1 as a symbolical variable.

Answer 1

[Andriy Kavetsky]

You should specify the variable theta_1 using next command

>> syms theta_1

Answer 2

[Jay]

I found one issue so far. I have downloaded the trial version and installed it but don't know how to activate it.

[Andriy Kavetsky]

So you have another problem.

[Jay]

It would seem so, I will write another question and return back to this if I still I have an issue.

If not I will flag as solved.