30 Day to Launch Phone
In other blogs I have mentioned that DirectMath (where XNAMath has moved to) can only be accessed by C++. Sooooo, just how do you use this in your C# code, etc. Well you would create a Windows Runtime (WinRT) component.
A simple walkthrough can be found at: http://msdn.microsoft.com/en-us/library/windows/apps/hh441569(v=vs.110).aspx (which is a good tutorial)
Then you can use the directmath stuff in a MetroStyle app.