I have problem with usage of solve for the solution of the system of six and eight symbolic equations. I need to get expressions for variables: R__xl, R__xs, R__xsi, R__zl, R__zs, R__zsi, dbeta__l(t), dbeta__s(t). I tried to find solution for 8 equations, but I got the message: Warning, solutions may have been lost. I thought that the system is non-linear and tried to solve it for six variables (R__xl, R__xs, R__zl, R__zs, R__zsi, R__xsi), in this case equations are linear, but Maple ignored the solve command and did not give a solution or error. Could someone help me with this problem?

Quasi-static.mw

I try to take a partial derivative of compound expressions. Usage of diff, Diff, substitution variables instead of time-variant variables (subs) couldn't help me.

Download DiffExpr.mw

Should I use implicitdiff? If yes, how does it work?

Also, I don't understand, why the derivative of theta_l is displayed so strange, as if the derivative is taken from the index l?

P.S. This question is a continuation of my last topic: https://www.mapleprimes.com/questions/229551-Operations-On-Several-Defined-Functions

May be a question is simple, but I'm beginner in Maple and I didn't find answer in Internet. I defined two functions: f(x,y)=sin(x)*cos(y) and g(x,y)=sin(y)*cos(x). How can I calculate third function v(x,y)=f(x,y)-g(x,y)? Answer of this operation should be: v(x,y)=sin(x-y).