I'm not a great fan of ripping wide boards down and gluing them back together, but flattening a wide board that is cupped or twisted, or both, more often than not results in the loss of a lot of material. You end up with a much thinner board than you started with. Less material is lost flattening narrow boards. For this reason, it sometimes makes sense to rip a wide board into narrower pieces before flattening it and then gluing it back together. Be aware, though, that you must re-joint the edges after the board is flattened to make sure it goes back together flat. The original edges are no longer square with the face of the board after it is flattened. With a board the size of yours, the process would be easier if you cut the big board to rough lengths first.
If you don't have a jointer, you can get a straight edge on you table saw by attaching a straight board to your wide board with the straight edge extending beyond the wide board's edge. Run the straight edge against your table saw fence, then turn the board around and rip the other edge parallel. Again, this is a lot easier if you cut your wide board to rough lengths first.