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─────Run-Time Library───────────────────────────────────────────────────────
 
     The acos, asin, atan, and atan2 functions return the arccosine,
     the arcsine, and the arctangent values of <x>, respectively. The
     argument <x> is specified in radians. The atan2 function uses the
     signs of both arguments to determine the quadrant of the return
     value. The functions, argument ranges, and return value ranges are
     listed below:
 
     Function     Argument Range     Return Value Range
 
     acos         -1 to 1            0 to π
     asin         -1 to 1            -π/2 to π/2
     atan         No limit           -π/2 to π/2
     atan2        No limit           -π to π
 
     The 8087 family of numeric coprocessor chips supports the 80-bit
     precision floating-point data type. Beginning with Microsoft C
     version 6.0, the long double functions, whoses names end with 'l',
     map the C long double type into this 80-bit, 10-byte form. Unlike
     the regular floating-point functions (such as acos), which accept
     and return values of type double, these long double forms (such as
     _acosl) accept and return values of type long double. In all other
     respects, they are identical to the regular functions.
 
     For the acos and asin functions, <x> must be between -1 and 1. If
     <x> is less than -1 or greater than 1, acos and asin set errno to
     EDOM, print a _DOMAIN error message to stderr, and return 0.
 
     The atan2 functions are well defined for every point other than
     the origin, even if <x> equals 0 and <y> does not equal 0.
 
     If both arguments to atan2 are 0, the function sets errno to EDOM,
     prints a _DOMAIN error message to stderr, and returns 0.
 
     Error handling can be modified with the _matherr (or _matherrl)
     routine.
 
     Return Value
 
     The return values for these functions are described above.
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