Help debugging a symbolic expression error

I'm trying to create a symbolic expression but don't fully understand the error I get. Code and error below.

syms l t b
f(l,t,b)=l((t/b)-(sin((2*pi*t)/b)/(2*pi)));

And the error:

Error using sym/subsindex (line 737)
Invalid indexing or function definition. When defining a function, ensure that the arguments are symbolic
variables and the body of the function is a SYM expression. When indexing, the input must be numeric, logical,
or ':'.

Error in sym/subsref (line 776)
            R_tilde = builtin('subsref',L_tilde,Idx);

I've tried making smaller expressions with syms variables and constants to eliminate the possibility that constants can't be used.

Answer 1

[Star Strider]

You’re missing a multiplication operator. MATLAB does not recognise implicit multiplication.

syms l t b
f(l,t,b) = l*((t/b)-(sin((2*pi*t)/b)/(2*pi)));
            ↑ ← INSERT ‘*’ HERE

That runs without error.