1

What is the difference among these?

Russian businessmen have been trying to work out what provoked Mr Putin.

Russian businessmen have tried to work out what provoked Mr Putin.

Russian businessmen are trying to work out what provoked Mr Putin.

3

"Russian businessmen have been trying to work out what provoked Mr Putin." is an example of Present Perfect Progressive tense - they have been trying in the past and this has continued up to the present, and may continue into the future.

"Russian businessmen have tried to work out what provoked Mr Putin." is the slightly simpler Present Perfect tense - they have been trying in the past and this has continued up to the present. It implies that they have now stopped trying.

"Russian businessmen are trying to work out what provoked Mr Putin." is Present Progressive tense, which means they're trying now and will continue to try in the future. It doesn't say anything (positive or negative) about whether they tried in the past.

So, you could summarise each as a group of past, present and future "trying":

"have been trying" -> past, present, future

"have tried" -> past, present

"are trying" -> present, future

eg http://leo.stcloudstate.edu/grammar/tenses.html

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