have you ever put your trousers in the washing machine and then remembered there was alarge bank note in your back pocket?请问remembered在这是一个动词,为什么做了主语,然后there was不也是主语吗,我记得一个句子只能有一个主语对吧,在这不矛盾吗,或者remeber在这里动词开头,句子不是不能动词开头吗,请高手详解这是什么语法现象

你的理解有误。
在这句子中，remembered的主语是you,但这里是承前省略了，remembered为谓语。
一个单句有一个主语，一个复句就不止一个主语了。
there was a large bank note in your back pocket为remembered的宾语从句。
相信你能理解赞同吧！祝你进步！

remembered在这是一个动词，是并列谓语 后面是省略that 的宾语从句 作remembered的宾语

remember there was ~~~是一个祈使句，省略主语。remember （that）there was a bank note in your back pocket .remember后引导宾语从句，省略that

remembered 在这里不是句子主语。整个句子是由两个并列句子组成的，由and then连接。第二个句子和第一个句子共用Have you ever这个开头，主语都是you，所以被省略了。完整的句子是这样的：
Have you ever put your trousers in the washing machine and then have you ever remembered there was a large bank note in your back pocket?

Have you ever put your trousers in the washing machine and then remembered there was a large bank note in your back pocket?这句话是由and连接的两个并列句,是可以差分成：1.Have you ever put your trousers...

remember是并列put 作动词的啊，同一个句子里不矛盾的