It is not clear what you are trying to actually plot.  Your expression is not syntactically correct Mathematica code. Perhaps it will be easier to understand if you use the formatting tools for this website's interface to place Mathematica code in its own area rather than in-line.  Also show your plotting expression so that we know what you are trying to attempt.... the more information you supply the easier it will be to figure out your problem.

But one thing that I notice right away is that you are using == rather than = in your assignment to A^2.  But also it is incorrect to assign a value to an expression such as A^2...  you must assign to a atomic parameter.   Thus if your paramter is "f" and it is assgined to an expression as follows (note thex in the arguments of the trig functions)


you can plot as follows: