In the new Ubuntu 18.04:   What's the default GCC version (with which the binaries were built)? What GCC versions are available as separate packages (and what minor version is installed if I install GCC 4, 5, 6, 7 or 8 respectively)? What Clang versions are available as separate packages (and what minor version is installed if I install clang 4 or 5?)   I can't find this in any release notes (and I don't want to have to install just to check.)
How can I check the version of the available package in the Ubuntu repositories without installing it?
What is momentum really? How to get Intel Dual Band Wireless-AC 3168 work on Ubuntu 16.04? could you help me on this integral ? $$\int \frac{1}{\cos(x)}\,\mathrm dx$$ Here's what I've started : $$\int \frac{1}{\cos(x)}\,\mathrm dx = \int \frac{\cos(x)}{\cos(x)^2}\,\mathrm dx = \int \frac{\cos(x)}{1-\sin(x)^2}\,\mathrm dx$$ Now, I did : $u = \sin(x)$, so $\mathrm du = 1$. Now I have : $$\int \frac{\text{???}}{1-u^2}\,\mathrm du$$ But at this point, I think I did the most of the job but I'm stuck. Could you help me to solve this integral please (to the integration by substitution at the end) ? Thanks EDIT : Now I follow the steps and I got : $$\int \frac{1}{1-u^2}\,\mathrm du$$ Doing the partial fraction I got $A = 1/2$ and $B = 1/2$. So basically I have : \begin{align} &amp; \int \frac{1}{1-u^2}\,\mathrm du = \int \frac{1/2}{1+u}\,\mathrm du + \int \frac{1/2}{1-u}\,\mathrm du \\[8pt] = {} &amp; \frac 1 2 \left(\int \frac{1}{1+u} \, du - \int \frac{1}{1-u} \, du\right) \\[8pt] = {} &amp; \frac 1 2 \ln\left(\frac{1+u}{1-u}\right) = \ln\left(\left(\frac{1+\sin(x)}{1-\sin(x)}\right)^{1/2}\right) \\[8pt] = {} &amp; \ln \left(\frac{\sqrt{1+\sin(x)}}{\sqrt{1-\sin(x)}}\right) = \ln\left(\frac{\sqrt{1+\sin(x)}}{\sqrt{\cos(x)^2}}\right) \\[8pt] = {} &amp; \ln\left(\frac{\sqrt{1+\sin(x)}}{\cos(x)}\right) \end{align} Here's what my teacher got :  What's wrong with what I did ? Did I miss something ? Why is feed-forward mechanism used in hash functions? The compression function of SHA-1 when used in Davies-Meyer mode adds its input to the chaining values at the final step. For the first message block, the IV is used as the input and in the next step, the previous block's output (as specified by Merkle-Damgård) is used. These values are fed to the last round of the compression function.  Why would removing the feed-forward part (i.e.,the final step where the input value is added to the result to get the final output) make the hash function insecure? Apart from the fact that the compression function would not satisfy desired randomness properties (being a permutation for each fixed message). I started learning Bash a couple of days ago.  I'm trying to obtain an exit status of grep expression into a variable like this:  check=grep -ci 'text' file.sh   and the output that I got is   No command '-ic' found   Should I do it with a pipe command? If we map every integer to a string that represents a rational number, and produce a number different from all the ones listed, we are essentially following Cantor's algorithm. But why does it not apply? Is it because we can't be certain that the number produced is a rational number? Are there names for consonant-shifts when suffixes are added? Minecraft 1.7.4 server issues with loading world What is a word for getting an award in a competition or being one of the top three? I am writing about a competition I won in which I got third place. I want to say that I am the first out of my school to get an award in this competition, with a third place award but that sounds a little bulky. What would be a short phrase or word to describe this. I am thinking maybe I can say "I placed in the competition" but I am not sure that will work. What happens if there is a security problem in a package in the universe repository four years after the 12.04 LTS release; will the package be updated from upstream, patched, or left alone?  It's my understanding that the "5 years of support &amp; security updates" applies only to the core of Ubuntu -- anything in Main repository.  Not for things in the Universe repository.    For a more specific example -- if I install Ruby now, and want to use it for the next several years on 12.04 and it has a security vulnerability; while this might be patched in the upstream (so I could always download the latest from their website and compile it myself or use a PPA), will this upstream fix be migrated into the precise package repositories? What about backports? How quickly is antibiotic resistance lost? Formula for calculating $\sum_{n=0}^{m}nr^n$ PSTricks error "Undefined control sequence  \c@lor@to@ps" "Outside" or "outside of"? How do I get HTML5 h.264 Video working on Firefox? According the the , h.264 video should now be working in Linux.  It does also say the appropriate gstreamer plug-ins need to be installed.  Does anyone know what these are?    I used this  and the  to verify that h.264 support works in Google Chrome on my Ubuntu 12.04 64-bit, but does not work on Firefox 26. Find the nilpotents in $\mathbb{Z}_3[x]/(x^2-1)$ Chatroom owners can star their own messages I was able to star my own message by pinning it and unpinning it.  Pinning a message adds a star, even to your own messages, but when the pin is removed, the star remains. Did Obi-Wan Kenobi ever become more powerful? In Star wars: IV A New Hope, Obi-Wan says to Darth Vader:     You can't win, Darth. If you strike me down, I shall become more powerful than you could possibly imagine.    What did he mean by this? Was he bluffing? Was he alluding to him being able to help Luke as a Force Ghost? Or was he talking on behalf of The Force? When a user without editing privileges suggests an edit to the post, a banner gets displayed until it is reviewed. Can the banner also provide a link to the Suggested edit? For example, I made an edit to a post on Unix&amp;Linux.SE. Can the banner also link to my ?     I know I can access the link through my Profile → Activity → Suggestions. But linking it directly on the face of the post would have immense benefits:  I have been a prolific editor on Ask Ubuntu (my first encounter with Stack Exchange Network) with a lot of Rep derived through Suggestions. I didn't get to know about these suggested edit links until very late (I guess I already had got about 400 edit suggestions approved by the time this came to my knowledge).  This means I didn't know about  when it mattered the most.  I never got to know why my suggestions got rejected because of my ignorance.  This would help reduce the barrier between Reviewers and Editors.  This would also help in case of Anonymous edits. Right now, there is no way an anonymous editor can access it unless the edit gets approved and he comes back to go through the Revision page of that particular post in order to access the Suggested Edit Review link. If the edit gets rejected - it's the end of the road for that anonymous editor. I just made an anonymous edit on one of the SE sites where I don't have an account and already feel like it's the end of the road for me since I just can't access the review link unless it gets approved.    Possibly also expand the banner to mention that they can also access the link to the suggestion via Profile → Activity → Suggestions. What issues / pitfalls must be considered when overriding equals and hashCode?