      double precision function dacos (x)
c may 1980 edition.   w. fullerton, c3, los alamos scientific lab.
      double precision x, pi2, dasin
      external dasin
      data pi2 / 1.5707963267 9489661923 1321691639 75 d0 /
c
      dacos = pi2 - dasin(x)
c
      return
      end