I am from Brazil, this means that my vocabulary for english is very poor, in relation to my vocabulary in portuguese - which is my native languange. Sometimes when I ask stuff, I try to search some terms about my interest first and then I give up, sometimes people come up and say: "This is a duplicate" or "this was already asked before". When I read the title of the question given by MSE users, it's usually something I'd never think about asking. So I believe it's better to ask it, if someone points it as a duplicate I can vote to close or delete it.
As long as you made an honest effort to search first, there is no shame in asking what turns out to be a duplicate. In addition to the built-in search, you should try Google search with the operator
site:math.stackexchange.com -- it often brings up more relevant results.
It is usually better to leave duplicates in place, marked as such, instead of deleting them. Later, someone may also be looking for the keywords in the title of your version, as opposed to the answered version. By the way, I see only two duplicates among your questions, versus six closed for other reasons. So it does not look like you have a major duplication problem.
$\begingroup$ I agree with this, and will add one thing: if you really think there should be a question like yours that was already asked, you can always post in the chatroom a short descriptor of your problem, and ask if anyone would help you perform a cursory search to see if it's a duplicate. I know that I would be more than willing to help out, but I'm not in the chatroom as frequently as I have been. $\endgroup$– apnortonDec 10, 2013 at 3:25
2$\begingroup$ I think part of the issue is not all titles are good. I often see a question that, when i look the title, seems almost completely unrelated. I can only imagine how this must appear to a non-English speaking person. $\endgroup$ Dec 11, 2013 at 16:37
1$\begingroup$ Adding onto that, I personally don't see a problem with a duplicate if there's a reason that the person couldn't find it (for example, if the topic is really obscure, or simply because the asker didn't know the right term to search). It's still a duplicate and ought to be closed, but I'd see it in a better light than a duplicate that arises because the asker was too lazy to search. $\endgroup$ Dec 17, 2013 at 22:52