/sys$common/syshlp/helplib.hlb RTL Routines, MTH$, MTH$xACOS, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 cosine

    OpenVMS usage:floating_point
    type:         F_floating, D_floating, G_floating
    access:       read only
    mechanism:    by reference

    The cosine of the angle whose value (in radians) is to be
    returned. The cosine argument is the address of a floating-point
    number that is this cosine. The absolute value of cosine must
    be less than or equal to 1. For MTH$ACOS, cosine specifies an
    F-floating number. For MTH$DACOS, cosine specifies a D-floating
    number. For MTH$GACOS, cosine specifies a G-floating number.