acos
====

.. qcs:function:: acos(x)
    :category: math

    :param x: series or numeric value 
    :type x:  :qcs:type:`series` or :qcs:type:`numeric`
    :returns: same type as **x**

    Returns the arccosine in radians in the range :math:`[0,\pi]` 
    of a number in the range :math:`[-1,1]`, **nil** otherwise