Define a function using symbolic constants

Question

I want to calculate the derivative and find critical points of the following function:

$\begin{equation} \frac{(w+w_s)(w^2+w_s^2)L^2C^3}{(wR^2C+(w^2 LC-1)^2)(w_s R^2C+(w_s^2 LC-1)^2)} \end{equation}$

Here's the code snippet:

f[x_] := ((x + ws)*(x^2 + ws^2)*L^2*
    C^3)/((x*R^2*C + (x^2*LC - 1)^2) (ws*R^2*C + (ws^2*L*C - 1)^2))

the error message is

SetDelayed::write: Tag Times in ((C^3 L^2 (w+w_s) (w^2+w_s^2))/(((-1+LC w^2)^2+C wR^2) (C R^2 w_s+(-1+LC Pattern[<<2>>]^2)^2)))[x_] is Protected.

maybe since there are so many symbolic constants like R,L,etc', mathematica can't interpret it. I tried looking online and in this forum, but I probably didn't formulate my question right, since I don't know how the "symbolic constants" I referred to, actually called in mathematica.

I hope I didn't miss any relevant posts, I'm new to mathematica, this is my first use.

Thank you for your time and attention