question about symbolic/numerical mixing



  Hi all. I'd like to use maxima to do a mix of symbolic and numerical
calculations. I mean something like:
-> solve a general problem, an find i.e.
a=b-c
-> then evaluate in a specific case (b:10, c=3)
a=7

  I can do it and all seems fine, but whit trigonometric functions. In
example, i get:

(%i9) F3:tan(40*%pi/180);
(%o9) tan((2*%pi)/9)

(%i10) eq2:F4-'F3=0$

(%i11) eq2;
(%o11) F4-F3=0

(%i12) linsolve(eq2,F4);
(%o12) [F4:F3]

(%i13) F4;
(%o13) tan((2*%pi)/9)

 what i'd like to have is:

(%i13) F4;
(%o13) .8390996311772799

I mean, what i get with F4,numer but assigned to the variable. It's not
too confortable doing each time (with each variable!)
F4:ev(F4,numer)

  So, there's is a way to do something like
evaluate_all_numerically:true/false ?

Thanks,
  Giovanni