When we remodeled our house, we used a drywall trick that eliminated taping the obtuse angles formed by walls and sloped ceilings. Instead of creating a joint at this line, we scored the paper on the back and broke the gypsum so that only the face paper remained intact. We kept this hinged piece narrow, about 2 in. on either side of the break. Nailing up this sheet was a bit awkward, but it gave us flat-taped joints on either side that we were able to deal with easily.
Steve and Becky Benton, Des Moines, IA