I recently came across this question which was closed as being a duplicate. When I read the linked source question, it was not a literal or even particularly specifically close duplicate, but in all fairness did present a discussion of principles which could be used to solve OP's question. However, the OP of the closed question is a new user, and as such might be expected not possess the mathematical savvy to both (a) abstract the relevant principles from the cited question, and (b) apply them to his specific case. The very language of OP's question seems to confirm such a view.
It further seems to me that if the criterion for closing a question as a duplicate is simply that the relevant principles have been laid out in previous questions, then almost all questions will be duplicates, or all answers can simply refer the OP to a relevant textbook. This seems to me to be an awfully ungenerous criterion, especially for novice question posers.
What is the community consensus on when a question is sufficiently addressed in prior posts to be deemed a duplicate? Further to that query, how much expertise ought the OP be credited with when the linked duplicate is written at a somewhat higher level of mathematical language and achievement than is evidenced in the posed question?