Question about "말했잖아요"

sometimes I heard Koreans said "말했잖아" what does the "잖아" means?

<Answer>

1. First Answer 

-잖아

You must already know that, right?

말했잖아.

I told you, you must already know that right?

2. Second Answer

it's like "you know" as a reminder, expressing that the listener should already know what the speaker is saying. like if someone says they're cold, they might say 겨울이잖아, "you know it's winter" as a reminder/explanation

3. Third Answer

See 1: https://forum.wordreference.com/threads/%EC%9E%96%EC%95%84-%ED%96%88%EC%9E%96%EC%95%84.1557424/

See 2 : https://www.italki.com/post/question-103333?hl=ko