Dear Mietz,
 
The original query relates to Question Tags, or Tag Questions. 
 
𨯗n A 𩗗 of English Grammar and Usage�, says, (slightly
abbreviated), 𨯗 tag question is a little
question we add at the end of a STATEMENT�.
𨧻ts subject matches the subject
of the statement�.
𨧻ts auxiliary, (or be) matches the auxiliary, (or be) in the statement, except that:
i)                    "If the
statement is positive, the tag is negative. 
If the statement is negative, the tag is positive�
ii)                  
𨧻f
there is no auxiliary or be in the
statement, we use do as the
auxiliary in the tag question�.
孏he
Tag Question invites the hearer to respond to a statement�.
幞egative
Questions expect a 𩂱es� answer,
Positive Questions expect a 𤨩o�
answer�.  
 
Here are some of my examples, with my underlining:
 
㛝ou do have enough money for the bus, don㦙 you?�
𨧻t𠏋 very warm.  You don㦙
need 2 overcoats, do you?�
㛝ou have remembered your passport, haven㦙 you?�
㛝ou haven㦙 forgotten your camera, have you?�
㛝ou are Russian, aren㦙 you?�
㛝ou aren㦙 tired, are you?�
㛝ou dance frequently, don㦙 you?�
㛝ou don㦙 dance the waltz, do you?�
㛝ou like your teacher, don㦙 you?�
 㛝ou don㦙 like bananas, do
you?�
 㛝ou attend Peking University, don㦙
you?�
㛝ou don㦙 attend University on a Sunday, do you?�
 
 
㛝ou can swim 1 kilometre, can㦙 you?�
㛝ou can㦙 swim 10 kilometres, can you?�
𨧻f you tried, you could swim 5 kilometres, couldn㦙
you?�
𡌃ven If you tried hard, you couldn㦙 swim 20 kilometres, could
you?�
 㛝our Dad has given you
permission --- you may come to the disco, mayn㦙 you?�
㛝ou mightn㦙 have enough money for your holiday, might
you?�
㛝ou must eat, if you want to be healthy, mustn㦙 you?�
㛝ou mustn㦙 eat too much junk food, must you?�
㛝ou ought to get plenty of sleep, oughtn㦙 you?�
㛝ou𠆫e so excited, you shan㦙 be able to sleep tonight, shall
you?�
㛝ou shouldn㦙 drink too much, should you?�
㛝ou will be a good boy and go to sleep, won㦙 you?� 
 㛝ou wouldn㦙 tell your
Father, would you?�
 
In the context of this query:
㛝ou must trust me, mustn㦙 you?�
 
I hope that I have helped you.
 
Les