Question: "Error, (in int) wrong number (or type) of arguments"

After fixing the problem outlined in a previous post, I seem to get another error that I can't explain. 


"Error, (in int) wrong number (or type) of arguments" is the product of defining a function 'u(r,theta,t)' and then defining each of its components. 


I've attached the file here as well. Could someone help with troubleshooting?


Also, I'm having trouble with the following concept. If I have this function 'u' and one of its components is, say, 'A', should I define 'A' as a function or a constant? 'A' does have variables like 'r','theta', and 't' and it also has the integers 'k' and 'm' (for the infinite series later on). 


Thank you. 

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