Can you post the code which you are trying to run?
If you are talking about the funtionality available in System::Math then it depends what type of project you have created. If you are using a Win32 Console Application then this is native C++ but if you are using a CLR Console application you just need to make sure that
Code:
using namespace System;
is at the top of your file, which should be there automatically in a CLR console application.