He is unhappy,isn' the?
1 带否定前缀的句子变反义疑问句,疑问部分还是用否定形式.即否定前缀不能视为否定词,其反意疑问句仍用否定形式.
It is impossible, isn't it?
He is not unkind to his classmates, is he?
2 而表示否定意思的词语/组变反义疑问句,疑问部分用肯定形式.比如陈述句含hardly,scarely,barely.never.seldom.little...和半否定词时,反义疑问句用肯定形式.
This meeting is unimportant,isn`t it?
完全可以推广到所有带有un、 dis等开头的单词中去.
http://blog.sina.com.cn/s/blog_48f2f3cb010008jo.html(绝对经典)