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 Nov 9 revised Interpreting division added 37 characters in body Nov 9 answered Interpreting division Nov 9 comment How can I solve this system? Plugging the 1st and 2nd equations into the 3rd, we get a quadratic equation for y. Nov 9 revised Hard algebra problem added 351 characters in body Nov 9 revised Hard algebra problem added 351 characters in body Nov 9 revised Hard algebra problem added 158 characters in body Nov 9 revised Hard algebra problem deleted 2 characters in body Nov 9 answered Hard algebra problem Nov 9 comment How could we find the largest number in the sequence $\sqrt{50},2\sqrt{49},3\sqrt{48},\cdots 49\sqrt{2},50$? Note that if the original question is for example $n\sqrt{50-n}$ instead of $n\sqrt{51-n}$, no integer $n$ satisfies the equality of the AM-GM inequality; in that case, a more careful evaluation, such as that used in Jyrki Lahtonen's answer, is needed. Nov 8 awarded Nice Answer Nov 8 accepted Calculating the probability that a cord makes a knot Nov 8 comment Calculating the probability that a cord makes a knot Thanks so much, that's what I'm looking for. If you post your comment as an answer I'll accept it. Nov 8 answered How could we find the largest number in the sequence $\sqrt{50},2\sqrt{49},3\sqrt{48},\cdots 49\sqrt{2},50$? Nov 7 comment Is there a good online dictionary/encyclopedia for mathematics? If you read Japanese, the most recent (Japanese 4th) edition of the Encyclopedic Dictionary of Mathematics has an accompanying CD-ROM that contains PDF files of the 4th and 3rd (equivalent to English 2nd) edition, which I find extremely convenient. (But of course they are not for free.) Nov 7 comment Proving that a binomial coefficient is the sum of two others math.stackexchange.com/questions/70190/… Nov 7 comment Higher order derivative of parameter curves $\frac{d^2y}{dx^2}=\frac{d}{dx}\left(\frac{dy}{dx}\right)$, and $\frac{d}{dx}(\cdots)=\frac{dt}{dx}\frac{d}{dt}(\cdots)$ Nov 7 revised Mathematics and Music added 36 characters in body Nov 7 answered Mathematics and Music Nov 7 asked Calculating the probability that a cord makes a knot Nov 5 comment How to add cosines with different phases using phasors $\sqrt{14+8\sqrt{2}}$, not $\sqrt{14+\sqrt2}$