Question

used todo的否定和疑问形式

Answer 1

used to do的否定形式是didn't use to do或usedn't to do。疑问形式是Did you use to do sth?

used to所表示的意思是“过去常常做某事”，强调过去发生的事，所以一般用于描述发生在过去的事情。

例句：My brother used to go swimming in the sea.

翻译：我哥哥过去常常在海里游泳。

区别

used to do和be used to doing的含义不同，be used to doing表达习惯于做某事的意思。

例句：I am used to having a cup of tea in the morning.

翻译：我习惯于早上喝一杯茶。

Answer 2

used to do的否定是didn't use to do或者usedn't to do.
He usedn't to be a teacher./He didn't use to be a teacher.
used todo的疑问形式是将used提前，或者在句首加did.
Used he to be a teacher?
Did he use to be a teacher?