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Imagine this: you have a piece of square stock wood: 4x4 say.
You want to cut it so that the square profile becomes an octagon.
So you tilt your table saw to 45o and move your fence across so that a single pass will cut off a triangular corner. You can then pass each side against the fence and voila! (Or possibly violin.)
The question is "how far should the fence be from the cutting edge of the blade?".
I did this this morning: I measured the stock, subtracted a bit under 4 cm, set my fence and cut a test piece.
It was spot on, each of the eight edges was the same length (with marginal variation because the stock wasn't exactly square but close enough) and I moved on.
Except I've been sitting here trying to work out the geometry, and just how I got my number from the original side length. And I have no idea how the heck I did it, because I didn't use geometry, I didn't use a calculator, and it's the first time I've done this. I just went "oh, it's 9.3cm, so I want 3.8cm edges, that's 6.5cm from the blade edge". And I was right.
But it's doing my head in trying to work out how I knew what the numbers were ... and why I was right first time ...
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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Cos you're inspirational and clever 
Life should not be a journey to the grave with the intention of arriving safely in a pretty and well-preserved body, but rather to skid in broadside in a cloud of smoke, thoroughly used up, totally worn out, and loudly proclaiming “Wow! What a Ride!" - Hunter S Thompson - RIP
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Says a man who has never met me ... 
My brain is screaming "0.707" at me, which is half root two, so it's probably bloody obvious Pythagoras, but I'm damned if I can see it. Or do square roots in my head. 
I suspect this is going to keep me awake tonight.
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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I had a professor many moons ago, when he couldn't readily explain a particular step of a mathematical proof, would say with a smirk,
"it's IOTTMCO!" (Intuitively Obvious To The Most Casual Observer), and he'd move on.
"the debugger doesn't tell me anything because this code compiles just fine" - random QA comment
"Facebook is where you tell lies to your friends. Twitter is where you tell the truth to strangers." - chriselst
"I don't drink any more... then again, I don't drink any less." - Mike Mullikins uncle
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Draw as square. Now draw a 45 degree diagonal across a corner. The lengths of the triangle sides are 1, 1, sqrt(2). That hypotenuse has to be the same length as the edge of the square timber that does not get sawn off. So, in terms of the corner you saw off, the length of a given side is 2+sqrt(2) units. That means for a 4" square timber, your diagonal cuts need to be made approximately 1.17" from the edge. This gives a side of your octagon of about 1.65 inches. e.g 1.17 + 1.65 + 1.17 = 3.99
Keep Calm and Carry On
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This how I visualised it, draw your 4cm square, then draw another 4cm square directly over the top of the first but at 45 degrees rotation. From here you can see that the dimension you need is the diagonal of the 4cm square minus 4cm side all divided by 2, which is (sqrt(32)-4)/2 =. 828cm
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I created a demo project named as BarEngineChart01. when I build it into .exe, my internet security software regards this exe as malware and deleted it. it triggered a full scanning and reboot.
what is the safe name for me to name my project?
diligent hands rule....
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'KillerVenenum' ?
"In testa che avete, Signor di Ceprano?"
-- Rigoletto
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I don't think your IS detects it because of the file name.
Check your .exe at
VirusTotal[^]
and keep us posted about the result.
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it is. this case happened several times.
I used Kaspersky suite...
diligent hands rule....
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It seems You do not want to understand.
Your IS may detect it because it is a new file and it has no rating for it or because of suspect behavior or something else.
The name itself is not the reason - but the content of the file may be suspect for your IS.
Rename it and you'll know it.
And scan it at VT as suggested before.
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renaming it does not help. I tried this way and it triggered disinfect and need to restart my computer...
I did some research and want to try this solution at the link.
diligent hands rule....
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 The poster didn't say that renaming the file would fix it, the poster said that the name of the file makes no difference and is not the reason it's being flagged.
The difficult we do right away...
...the impossible takes slightly longer.
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here is the message I quote from stackoverflow:
Quote: Kaspersky it's using the heuristic scan, a technology which checks the code behind for the patterns. Some pieces of the code they are used in the malware programs and it gonna say that they are viruses. I remember that once I've created a service to insert some MySql data for wordpress, he said it's a virus, another time used a geojson to draw a map and it was saying that it's a virus when I've added a piece of code to draw for each city a dot.
it hints that more dots can be suspicious...
diligent hands rule....
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Go into your AV software, and set your programming directory to not be scanned. That's what I had to do when I had Norton. Don't know about Kaspersky.
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Same with Sophos and McAfee
// TODO: Insert something here Top ten reasons why I'm lazy
1.
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very good to know...
diligent hands rule....
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In my last job, the employer insisted on running some malware detector (I am not able to recall its name right now) that all the time triggered on the system I was developing. So I declared a dummy string variable (and had to make a dummy modification to it to ensure that it wasn't optimized away) to disturb that bit pattern in my code that the virus scanner mistook for a virus signature.
Every few code updates, other changes made the offending bit pattern again reappear in my code. So I had to delete from or insert into that dummy string a few characters to disturb the 'virus signature' bit pattern again. (After a while, I ended up with having two string, commenting out one, uncommenting the other. It never happened that the virus scanner gave me trouble with either alternatives and no other code changes.)
I complained so loudly about this that I was told that the virus scanner could be configured to bypass any given directory, and they could set it up so that the directory where I generated the system during development not scanned. Production versions were generated in another directory, which they refused to except from virus scanning. So several times, the first attempt at production build caused a virus warning, and I had to rebuild after commenting and uncommenting the alternate dummy string. We did not make releases every month, so this was considered acceptable, as long as the daily development work didn't require daily rubbing the virus scanner behind its ear to keep it from biting.
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thanks for your story![Rose | [Rose]](https://www.codeproject.com/script/Forums/Images/rose.gif)
diligent hands rule....
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Immediately get rid of any so-called anti-malware that is so amateurish that it takes this drastic an action as a result of something it failed so badly at.
[Edit]
Oh. Kaspersky strikes again, I see.
A few decades ago my employer had us use Kaspersky, and I remember having to tell it to skip my dev folder for reasons similar to yours.
Nice to see that decades later they're still dealing with this. How long can they repeat this before they realize their approach to scanning should be abandoned?
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In times like this I would not use an IS / AV that is related to Russia 
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Don't forget that Kaspersky is a Russian company. The problem here is that the Russian Government can force Kaspersky to turn over anything they collect, and likely does.
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Just remember, it's only in math classes where you can buy 64 watermelons and no one wonders why.
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