Thomas
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 Feb 29 comment Can every integer greater than 5 be written as the sum of exactly one prime and one composite? Alternatively you can also think of it this way: there's clearly always a prime $p$ between 1 and your integer $n$, and there's a good chance that $n - p$ is not prime; so clearly the problem isn't hard. it shouldn't be hard to work out possible values of $p$ that will systematically work for all $n$. Dec 31 comment V.I. Arnold says Russian students can't solve this problem, but American students can — why? Am I the only one who had to look up what an "altitude" meant in this context? I've only ever seen it referred to as the "height" of a triangle, as in the usual "area = base * height / 2" formula... is this US-specific terminology or something? Nov 10 comment Are there any situations in which L'Hopital's Rule WILL NOT work? @JoelReyesNoche Only if said conditions are both sufficient and necessary! Strictly speaking a rule may still work outside of its prescribed conditions either because they are not strict enough, or just by sheer luck. :) Oct 24 comment Write a formula as a sum of fractions with constant numerators For more information about this type of transformation search for "partial fraction decomposition" on google. Aug 26 comment Is 4 the second or third digit of pi The most versatile approximation in my opinion is 3.14159265. Easy to remember, pronounce (314 159 265), type out, extremely accurate, but not long enough to make it weird. Aug 19 comment What is the sheafification of the presheaf of the one point compactification? tongue twister! Aug 4 comment A problem in integration. @user258250 $\frac{-1}{2} \cos(2 \pi/6) - \frac{-1}{2} \cos(0) = \frac{1}{4} = \sin^2(\pi/6) - \sin^2(0) = \frac{1}{4}$ Jun 7 comment What is the difference between necessary condition & sufficient condition? That's right; but your second sentence contradicts this: you wrote that if A' is a sufficient condition for B then A' must exist in order for B to occur, which is not true. That's why I asked if you had a typo Jun 7 comment What is the difference between necessary condition & sufficient condition? Typo? "Sufficient condition A′ means that A′ must exists in order for B to occur [...]"; wouldn't that mean that one must solve the Riemann hypothesis to get accepted into a prestigious university? Jun 3 comment Is this theorem already in existence? I think it's usually introduced to high-schoolers when factoring quadratics with integer coefficients: you expand out the product and get them to find two integers which add up to $s$ and multiply to $p$. May 27 comment Identification of a quadrilateral as a trapezoid, rectangle, or square Perhaps more importantly, why did your student not produce a counterexample (e.g. by drawing on the board) after her answer had been questioned? Possibly shyness/anxiety? (apologies if someone asked this before, did not read all the comments) May 11 comment RSA, cipher, Cryptosystem That's right (and we disregard $C_3$ because it's not needed, you only need two ciphertexts of the same plaintext encrypted with coprime public exponents to obtain a linear combination like Todd shows - 17, 19 and 21 are pairwise coprime so you could use $C_1$ and $C_2$, or $C_2$ and $C_3$, or even $C_1$ and $C_3$) May 11 answered RSA, cipher, Cryptosystem May 5 comment Notation (or Name) of the function which is 0 at x=0 and 1 otherwise This isn't "traditional notation" (nor simpler) like the question asked, it seems more like obfuscation than anything.... unless this definition from the Heaviside function allows one to derive nontrivial information about the function, it seems pointless. May 4 comment Result of solving an unsolved problem? puts tin foil hat on maybe the NSA has already found a constructive proof that P = NP... (just kidding, or am I?) Apr 27 accepted A quadratic polynomial bounded by another Apr 27 comment A quadratic polynomial bounded by another Thanks, I guess this settles it haha Apr 27 asked A quadratic polynomial bounded by another Apr 21 comment Determine if the following is surjective Just wondering, how come you used a greek eta symbol rather than a plain n? Not criticising, just curious if it has any special significance... Apr 20 comment How many scientists can survive? "hopefully clever enough" if they aren't, the 99 scientists die in confusion while the first one dies in vain.