"This is not your problem."
Translation:Это не твоя проблема.
Because you're referring to a random thing, you don't know the actual problem. If you'd say "this problem is not yours", it'd be эта проблема не твоя, because you're stressing: THIS is not your problem (but something else might be).
You use Ваша If you are talking to someone you dont know or someone older than you. Its more formal and respectful. Just like 'You' has its formal and informal addressing. So; Вы (you -formal) Ты (you- informal)
Good question. Unlike English an 'is' in Russian connects two nominatives.
It's her - Это-она (not её!)
But didn't they say in the tips and notes that negation is done with the genitive case?
I believe what they meant is actually the use of word 'нет', not any negation in general. E.g. Тут НЕТ проблемы - there is no problem here. In that case you do have to use genetive
I love the fact that, even though they seem so far linguistically, "problem" in both Portuguese and Russian is the exact same word.
Эта проблема - this problem Это проблема - this is a problem. This is (это) is invariable, while just the "this (этот, эта и это) chаnges according to gender and case.
Im learning too, buy I think it it because it says "this is" rather than "this".