Har du inga byxor? Jo, det har jag (!?)
This has come up in the timed practice, but it wasn't covered in the lessons. I really wish it were, because it is definitely something a bit different from all the simpler concepts in the lessons. I barely had time to jot it down so that I could look it up in the discussions!
Szczepanovich's explanation is excellent. As a Swede learning French I find that "Ja" and "Jo" seem to correspond perfectly to "Oui" and "Si".
Yes, I really appreciated it (and gave him a lingot)! All three of the explanations are great. And it's nice to know that you, as well as Szczepanovich and other native Swedish speakers, are keeping an eye on the comments generated by the Swedish course. Thank you!
How to confirm the negativity? example: Don't you have pants? No, I don't. Do we use nej or ja?
I think both "nej" and "ja" works to confirm the negativity. "Ja" seems to point to the correctness of the statement in the question ("yes, that is right"), while "nej" seems to confirm the lack of something ("no, i have no pants"). But there is some room for confusion if one is being vague.
Har du inga byxor? Nej, det har jag inte.
or in short:
Har du inga byxor? Nej.
I would never use "Ja" in this situation. It would be confusing.