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 11h comment Big O counterexample Please rephrase your question. Nobody here knows what you are trying to ask. 11h comment Is there any closed form expression for the following sum $\sum_{t=1}^T \frac{2^t}{t} = ?$ What's $E_i$ in your expression? 13h comment What kind of proof is this? @DionysiosGerogiadis Then you reached a contradiction and you have proven that it is not true that all squirrels have two tails. Once you assume something, a resulting contradiction can only disprove your assumption, not prove it. 13h comment What kind of proof is this? @DionysiosGerogiadis If Zeus exists, mount Olympus must exist (because it's his home). Mount olympus exists. Therefore, Zeus exists. 13h answered What kind of proof is this? 13h comment Integer solutions to $x^2-xy+y^2=1$ Wait, did you both ask the question and answer it? 13h comment What does it mean for transitive closure to be minimal? @paulpaul1076 I gave an example. The point is if you have a transitive relation $R$, and you take away one element, the resulting relation may not be transitive any more. In fact, that's the whole point of transitive closures: It's such a relation from which nothing can be taken away. 13h revised What does it mean for transitive closure to be minimal? added 562 characters in body 14h answered What does it mean for transitive closure to be minimal? 14h comment What does it mean for transitive closure to be minimal? I assume you are talking about relations? 15h answered Proving a basis in linear algebra 15h comment Quick Question - Complex Roots of Polynomials? This question is not perfect, sure, but guys, come on. It doesn't deserve the downvotes! 16h comment How many strings of six lowercase letters have at least one vowel? @barakmanos Well by that I mean I agree that there is a "laziness threshold" under which a question should not get any answers. I don't think this particular question is there, but if someone has a different threshold, then it's reasonable he would downvote the answers. 1d comment How many strings of six lowercase letters have at least one vowel? @barakmanos I think it's the "this question is so lazy it doesn't deserve an answer" kind of downvote. I almost agree with it. The OP has a test tommorow and only decided to study the stuff today, and wants full answers that will enlighten him... 1d answered How many strings of six lowercase letters have at least one vowel? Apr 21 comment Definition of limit convergence $9/(10^n)$ does not converge to $1$. Apr 21 comment Find real parametar $a,b,c$ such that function $f$ become convex function $f(x) = \begin{cases}ax^2+bx+c,& x<0\\1 ,& x \ge 0\end{cases}$ If $f$ is convex, it is also continuous. That tells you things about $c$. Apr 21 comment What's wrong when a particle is accelerating? @marcotrevi No, it isn't possible. You must understand that the Taylor series is only guaranteed to work locally even for analytic functions. If the function is locally $0$, then the series is $0$. Apr 21 revised What's wrong when a particle is accelerating? added 337 characters in body Apr 21 answered What's wrong when a particle is accelerating?