On the Internet, the author once encountered the following line of C$-$language code

PI $=2*$asin$(1\mathrm{.}0)$;

whose purpose was to define the constant $\backslash$pi $.$ In standard mathematical notation, that line of code can be described by

$\backslash$pi $=2$ sin$1(1).$

Under what assumption does the above expression correctly define the constant $\backslash$pi $?$