sb used to do sth.它的否定形式是什么?
其否定形式有两种，可以用didn't也可以用not:
1, He didn't use to get up early when he was young.
2, He usedn't to get up early when he was young.
3, There used to be a meeting on Monday, didn't there?
4, There used to be a meeting on Monday, usedn't there?