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.

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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

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[Category Command] | [Category Mathematics] |
[Category Syntax]