acos

# File lib/cmath.rb, line 257
  def acos(z)
    begin
      if z.real? and z >= -1 and z <= 1
        acos!(z)
      else
        (-1.0).i * log(z + 1.0.i * sqrt(1.0 - z * z))
      end
    rescue NoMethodError
      handle_no_method_error
    end
  end