acos (arc cosine) is one of the math commands available in expr, as well as in the tcl::mathfunc:: namespace as of Tcl 8.5.
It is a procedure which provides command access to the expr math function, taking the same arguments as the expr function and taking expressions as arguments as well.
One good use for acos is to get the constant Pi:
% expr acos(-1) 3.141592653589793 % tcl::mathfunc::acos -1 ;# In Tcl 8.5 3.141592653589793
| Category Command | Category Mathematics | Category Syntax |
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