How to draw by DrawLinePenned?

Jul 26 at 6:50 PM
I want to add thickness to a line.
I use C#, WPF.
I tried, but it doesn't work:
            WriteableBitmap writeableBitmap = BitmapFactory.New(500, 500);
            writeableBitmap.DrawLinePenned(10, 10, 50, 50, ?);