How to determine the components of a velocity vector undergoing a central force
Distribution of orbital velocities in a disk galaxy for N-body simulation?
Buster Blader the DDS did not affect Destiny Hero - Decider effect; why so? How come  with  set to dragons didn't stop 's effect from being activated? Are there some good overviews of basic facts about images and inverse images of sets under functions? What is the Python equivalent of Perl's chomp function, which removes the last character of a string if it is a newline? How do I check if a list is empty? Combinatorial argument for $\sum\limits_{k=i}^{n}\binom{n}{k}\binom{k}{i} = \binom{n}{i}2^{n-i}$ I need to show that $$\sum\limits_{k=i}^{n}\binom{n}{k}\binom{k}{i} = \binom{n}{i}2^{n-i}$$  I know that $\displaystyle \binom{n}{k}\binom{k}{i}$ is counting the number of ways to pick $k$ elements from $n$ and then $i$ elements from those $k$, so $\displaystyle \sum\limits_{k=i}^{n}\binom{n}{k}\binom{k}{i}$ is counting the number of ways to do that $\forall k$.  I know that $\displaystyle \binom{n}{i} = \binom{n}{n-i}$ and that $2^{n-i}$ is the number of elements in the power set for $[n]\setminus[i]$.  How do I show that both sides are equivalent? I'm stumped on this one. Could anyone give me a pointer in the right direction? When transiting between two flights, will my luggage be automatically transferred? Where are the Unity desktop wallpapers located? Please see the picture below. Where are the Unity desktop wallpapers located? Should flawed questions be closed immediately? Possible Duplicate:          Given a question that is not clear at first, which satisfies the criterion for being "not a real question":      "It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot   be reasonably answered in its current form."   should that question be closed immediately, or should the OP get a chance to improve the quality of his question.  My modus operandi is this: When I encounter a question which is "not a real question", I respond via a comment - I might ask one or more counter-questions (about the issue), I might comment that I don't understand the question. So, I let the OP know that his question should be improved. I then give the OP say 15 minutes to respond (and in most cases the OP does respond). However, if the OP doesn't respond, then I consider voting for "not a real question".  Is this how SO should work?   I have witnessed in the past several questions for which I saw potential, being closed immediately, and I wonder if that is appropriate.   Edit: Of course, questions that are duplicates should be closed immediately, and off-topic questions should also be moved / closed immediately. In this question I am specifically referring to those questions which "have potential" (which could be corrected / improved).. How could a raw, untrained Force user be so adept at using the Force? Everything that I seemed to know about the Star Wars universe indicated that in order to be successful at being a force user, the user required decades of training and experience.  Which is why I thought that the Jedi trained their pupils from birth to be force users. The lengthy training period was also why the Jedi council said Anakin was too old, and subsequently why Yoda said Luke was too old to begin the training. This can be seen in comparing Luke's raw abilities in the original trilogy compared to that of the Jedi in the prequel trilogy.   However, in The Force Awakens,      Rey not only fends off Kylo Ren, she comes very close to killing him outright, even though she had never even held a lightsaber before.   This happens not long after      she uses her Force persuasion power to escape prison, despite not even believing she was Force sensitive until that point.   It doesn't make any sense that the fight wasn't over in a matter of seconds. What am I missing? Was the singularity at Big Bang perfectly uniform and if so, why did the universe lose its uniformity? What is the difference between the dashed and solid attack bars? I was flipping through my Pokemon list to see which kind of attacks they had, and I notice there was a small different between the attacks. Some attacks contained a dashed blue bar where as others contained a solid blue bar.   What is the difference and significance between the two? Let $|A|=\alpha, |B|=\beta, |C|= \gamma$ be cardinals and $\beta \leq \gamma$. Prove $\alpha ^{\beta}\le \alpha ^{\gamma}$.  So from the given we know that there's an injection $f:B\to C$ and some functions $h:B\to A, g: C\to A$. We want to prove there's an injection $l_1:A\to C$. It appears that $f$ doesn't help here.  Trying to take representatives from $A$ and show they're in $C$ and there's an injection doesn't work so maybe the function should be $l_2: h \to g$ but I don't know how to work with it. Slope of geometry as `fac` input for cycles material I have a terrain with two materials going into a Mix Shader, I want the fac input to be the slope of the terrain. Steep parts should be one color, flat part another. I have a python list, say l  l = [1,5,8]   I want to write a sql query to get the data for all the elements of the list, say  select name from students where id = |IN THE LIST l|   How do I accomplish this? Why this :$\sum\limits_{n=1}^\infty\frac1{n\sin n}$ is not harmonic series and is convergent? I'm confused how this series :$$\displaystyle \sum_{n=1}^\infty\frac1{n\sin n}$$ is a convergent series as wolfram show  and it's not harmonic series in the same time .  My question here is:  Why this :$$\displaystyle \sum_{n=1}^\infty\frac1{n\sin n}$$ is not harmonic series and is convergent ? A very compact list in Beamer I would like to make a very compact list (e.g., itemize) in Beamer.  has been asked for an article-type document class; the answer uses the enumitem package, known to be .  My question is: How do I make the same compact list in the Beamer document class? As in the above linked question, I would like the list to have   No whitespace before list No whitespace after list No whitespace between lines Less indent before the bullet points How to disable internet search results in start menu post Creators Update? It  to disable internet search results in start menu searches before the Windows 10 Creators Update, but I've just clean installed a new Windows 10 Pro image and that setting is gone. Is there some way to disable it through editing the registry/etc? Display Blank when Referencing Blank Cell in Excel 2010 I have an Excel 2010 workbook that contains a number of individual worksheets. The cells on one of the sheets are linked to individual cells on two other worksheets in the same workbook.  I'm using a direct cell reference that essentially says that whatever value is entered into a particular cell on one sheet also populates cells on two other sheets.  I used the (=) function with the cell reference to accomplish this.  The issue I'm running into is that, even when the primary cell is left blank, the cells that populate from that primary cell will display 0, rather than remaining blank themselves.  I want the subordinate cells to remain blank if the primary cell they're linked to is blank. On any SE post one can use the backtick symbol ("`") in order to mark some text as being a piece of code, or computer output. For example: void main().  Is there a way to make use of "`" the same way in a LaTeX document? Program does not wait before output