Hello! I am doing my Extended essay about the maths involved in calculating your position using the GPS. I am reading a very complete book, but the maths are sometimes too hard or not enough deeply explained for my level and I am struggling to follow some parts. Here I post one page of the book where they derive a linear equation (14.8) which I can't finish to see where they get it from. I now understand that the weighting matrix entries are direction cosines but I don't really get how they derived that equation. Thank you.