I posed my first Math Stack question, earlier this evening. It was on the product of expectation values. I received an answer that enabled me to solve my problem by using Cauchy's Inequality. The respondent referred to Jensen's Inequality, a more comprehensive relationship than Cauchy's as I found from reading a Wikipedia article. To understand the Wiki article, I should have far more mathematical background than I do: measure theory, for example. Why not urge respondents to gauge the level of their replies to the level of the questioner? I am sure that my statement makes clear that I am not an advanced graduate student in mathematics. If I were, I would not have needed to pose the question in the first place.

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    $\begingroup$ Although Jensen's Inequality is applicable in more general measure theoretic settings, it can be stated simply as $$ \int_Eg(x)\,\mathrm{d}x =1\implies\int_E\phi(f(x))g(x)\,\mathrm{d}x \ge\phi\left(\int_Ef(x)g(x)\,\mathrm{d}x\right) $$ for $g(x)\ge0$ and any convex function $\phi$ whose domain includes an interval containing the range of $f$. Don't be overwhelmed by Wikipedia's generality, which is useful in more advanced situations; Jensen's Inequality is useful in less advanced settings, too. $\endgroup$ – robjohn May 11 '15 at 3:08
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    $\begingroup$ I must admit I find this question partly disingenuous. When the answer was posted to your question, you gave no context as to your background or what sorts of answers you were hoping for. The answerer gave a very natural answer that has the added benefit of being short enough to fit on a napkin. Afterwards, you edited your question and asked for Cauchy's Inequality. This seems like a good example of why it's good to clarify questions, give context, and what you've tried. $\endgroup$ – davidlowryduda May 11 '15 at 3:14
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    $\begingroup$ You asked the question, goedelite, but you may not be the only one to read the answer. Someone else might benefit from an answer that you don't understand. You might even benefit from it yourself, some day when you've learned more stuff. You don't have to praise the answer, but it's a bit small-minded to denounce it. $\endgroup$ – Gerry Myerson May 11 '15 at 3:19

In short, the answer is "because we don't exist to help only you." The purpose of StackExchange is not to answer every question someone has as they encounter them, but to produce a high-quality database of questions and answers.

You may want to read this meta question. We don't answer questions to help you; rather, we answer questions to help anyone who may have a similar question. As such, it's perfectly fine to answer with higher level mathematics than the person asking. Sure, most answerers will try to keep on the questioner's level, but there is no requirement to do so.

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    $\begingroup$ The two (by far) most upvoted answers of the linked question contain the statements: "...look at all this math I know..." (if level of answer is higher than implied math knowledge of OP), and "...the answer should always include a part with a mathematics level that seems understandable by the OP...". Other than selective reading, I find it hard to see how the linked question thus supports your answer here. $\endgroup$ – gnometorule May 11 '15 at 16:59
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    $\begingroup$ @gnometorule I wish I could write it off as "selective reading." To be honest, I looked up the thread and assumed I remembered what it said. :P Apparently, I was vastly wrong. I still hold my opinion, but I guess my link doesn't support it at this point. $\endgroup$ – apnorton May 12 '15 at 1:44

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