Formal:
* Determined
* Decided
* Resolved
* Finished
* Completed
* Terminated
* Ended
* Summarized
Informal:
* Wrapped up
* Finished off
* Called it a day
* Came to an end
* Reached a decision
* Made up one's mind
Specific to a situation:
* Negotiated (if referring to an agreement)
* Judged (if referring to a decision)
* Deduced (if referring to a logical conclusion)
* Discovered (if referring to finding a solution)
The best synonym will depend on the specific context of the sentence.