Merge pull request #2473 from edx/sylvia/documentation/BLD-787

Update warning for Math Expression Input problems

docs/en_us/course_authors/source/advanced_problems.rst

@@ -307,7 +307,7 @@ Studio, you'll use `MathJax <http://www.mathjax.org>`_ to change your
 plain text into "beautiful math." For more information about how to use
 MathJax in Studio, see :ref:`MathJax in Studio`.
 
-.. warning:: Math expression input problems cannot currently include any any kind of complex numbers. This includes negative numbers raised to fractional powers, such as (-1)^(1/2).
+.. warning:: Math expression input problems cannot currently include negative numbers raised to fractional powers, such as (-1)^(1/2). Math expression input problems can include complex numbers raised to fractional powers, or positive non-complex numbers raised to fractional powers.
 
 .. image:: Images/MathExpressionInputExample.gif
  :alt: Image of math expression input problem