Sasha, Вопрос такой сложен что еще не был решен. = The question is so complicated that it still was not resolved. --The question was not resolved at any time in the past. Вопрос такой сложен что еще не решен. = The problem is so complicated that it is still not resolved OR = . The problem is so complicated that it has still not been resolved. --The question is so complicated that it is not (has not been) resolved even now. ========== So, the problem is TOO difficult to HAVE BEEN SOLVED? The infinitive here modifies the predicate, i.e, the predicate adjective “complicated”. The English infinitive in this case expresses purpose or potential. “so that it can be” “In order to be” The question is too complicated to be resolved. = Вопрос слишком сложен (для того), чтобы быть решен. The question WAS too complicated to have been resolved. = Вопрос был слишком сложен (для того), чтобы был решен. Вопрос слишком сложен, чтобы решить /решать. = The question is too complicated to resolve. Of course the above are not the only possible translations. A lot depends on context.

The problem is too difficult to solve. "to have been solved" "to be solved" Both are wrong in this construction.

The fact that a problem has not been solved yet does not mean that it can't be. It implies only that it may take time and the problem is difficult. A very good example is Pascal's Last Theorem. This stated that you could not find three integer numbers, A, B and C, such that the sum of A raised to a power of N plus B raised to that power would equal C raised to N, for any N greater than 2. Everybody knew you couldn't find them, but nobody could prove it. It took two centuries before this problem was solve. Before that happened, many people were saying that it couldn't be solved. In conclusion, a problem may not be solved yet, it does not mean that it can't be solved - it just may take time.

I actually meant the translation of the sentence in Russian: Вопрос такой сложен что еще не был решен. The task is too difficult to have been solved. Translation with the Perfect Passive Infinitive or The task is too difficult to be solved. Translation with the Present Passive Infinitive. Which one transmits the thought better?

The problem is too difficult to be solved until now. People r working on it. They might be able to solve it at some point.