## Trying to derive a function with Geogebra but it wont give in, is there anyone experienced that could lend a hand?

This is the function: f(x) = ((((((1)/(2π))2)π)sqrt((((1)/(2π))2))-(1-((1)/(360)x)/(2π)(1))2)/(3)), in geogebra it looks like this: https://i.imgur.com/ngFKtPa.png

It’s the formula for determining the volume of a cone by cutting out an angle from a circle and forming the remaining part of the cirlcle into a cone. It is one hell to derive by hand and would probably take my sanity in the process, the original formula I had looks like this: https://i.imgur.com/B96Ds5n.png (O is the letter not the number), but since the formula containing V is essentially just a coefficient to O, and I’m determining maxes, I figured that I can make O to “1”, since the formula still behaves in the same relativity. THen I used “x” instead of “v” since geogebra is sometimes like that. But it doesn’t seem to work, any idea?

Sidenote, I’m uncertain if geogebra is taking the square root of only the area it covers, I would like it to square root this entire section: https://i.imgur.com/kIS1gJF.png

submitted by Nevin Manimala Nevin Manimala /u/dantellex

So hello people from reddit!

I’m a huge fan of card especially bmw’s and i came across this video (https://youtu.be/mPD0SkFz4Bw) now for months kve been trying to figure out if this is real or not people say its sped up but some thing just seem too normal to be sped up. I would love to find out more about this vehicle thanks in advance

submitted by Nevin Manimala Nevin Manimala /u/AceThugJr

## Suzuki Swift (2005+) automatic experiences?

Anyone have experience with the automatic transmissions in these cars? One has come up on my radar (150k ish kms, 1.3l AT for about 3.5k EUR) and I’d like to get some info on the reliability of the automatic transmission in these plus the manufacturer if possible.

submitted by Nevin Manimala Nevin Manimala /u/seinfeldforpresident

## OBD II suggestion?

I want to buy a reasonably good OBD adapter , I got a cheap one from china and it died creating havoc in the can bus line on my car (nothing was working while it was plugged in , now the air bags are flagged as not working because they didn’t answer once) , totally regret that now .

Anyhow, any good one? preferably something I can plug in my FIAT bravo 2008?

submitted by Nevin Manimala Nevin Manimala /u/emuboy85

## Is the amount of eponyms and shorthand notations in mathematics helpful ?

1) The context which makes me ask this (optional, but might give better insight into the question)

I’ve been musing on the difference between mathematics and computer science for a while, namely as to why I personally got along very well with the later but not the former.

There’s a famous quote I saw attributed to many people, about programming/CS is: “There are only two hard things in Computer Science: cache invalidation and naming things.”

And I think this quote represents the difference between CS and mathematics quite well, in that, programmers are forced to work in this “finite” space where concepts such as infinity and shape are replaced by concepts such as memory and accuracy. And that small detail obviously means the two go into completely different direction, since you can’t really talk about calculus or linear algebra or even basic things such as convergence and divergence in the discrete and finite world of computers.

But the other thing which strikes me to be quite different between CS and math, is that the former places a lot of emphasis on naming. Indeed, many people that have worked in the field will tell you that buggy code can be sniffed out based on the name of things alone, and that a decent paradigm for deciding how to write code, is to think in which way you can give things names which make sense (though I haven’t meet many practitioners of the former).

2) Some examples of the problems in naming

Is there something mathematics can learn from the field of computer science in terms of naming things by combining concepts and going for intuitive names, rather than shorthands and eponyms.

For example, it always struck me as weird that things like “The Laplace transform” existed, since I always thought it could just be called “The complex Fourier transform”, which doesn’t express the difference between the two perfectly, but it’s short, and it at least alludes to the contents of the concept of Laplace transform, at least, if one know what a Fourier transform is. Whereas, one could perfectly understand what a Fourier transform is, but, had he never heard of the Laplace transform, he may think he has reached uncharted waters when someone mentions it.

A better example of how omnipresent eponyms in mathematics are, I got whilst reading this paper:

http://www.iiisci.org/journal/CV\$/sci/pdfs/GS315JG.pdf

This is a simple comparison of various binary distance/similarity functions.. 76 of them to be precise, some very similar, some very basic, some very useless. But they all bare the name of a person, which makes understanding how they relate to each other, rather impenetrable… since you have only the equation to go by, the names are actively distracting you from the point. I’m quite sure, however, that all 76 functions (or at least a good percentage of them).

A similar point could be made about shorthand notation that losses all meaning to the “uninitiated”. For example, everyone knows what `+` means, almost everyone knows `x` stands for an unknown or free variable, not that many people know `ε` could mean a very small yet different from zero number… etc (there are more obscure things, but at this point I’d start to go into notations that are obscure because they are very domain specific). So isn’t there a point where it may be healthy to drop shorthand notation ? Not as in, switching `+` with `add`, but maybe switching `x` with `unknown`, most certainly switching `ε` with `very_small` or `tiny_nr` and switching `∇` to `grad`.

3) The actual questions I have

Is there justification for the heavy use of eponyms and shorthand notations in modern mathematics ? Do you think a “re-writing” of mathematics using more meaningful names is possible or desirable ? Do you see such a change coming in the future ?

submitted by Nevin Manimala Nevin Manimala /u/elcric_krej

## Scratches down to the bare metal – is primer necessary?

Apologies if this is the wrong place to post this. Yesterday I noticed that someone has scraped my car, and in parts it’s gone down to the bare metal. My car is over 10 years old and has its fair share of imperfections, so I’m not too concerned about how it looks. I’m mostly concerned about rust and any other permanent issues this might cause.

I have a can of touch up paint matched to my car’s colour, and was wondering whether it’s ok to paint it on directly. Also how quickly do I need to fix this up? My car is in a secure covered garage away from the elements, if that makes any difference.

submitted by Nevin Manimala Nevin Manimala /u/freswood

## Combining Z Scores by Weighted Average. Sanity Check Please?

I’m trying to measure how “exceptional” a particular observation is based on several attributes of that observation among a population of observations.

Each observation has several attributes, all numerical quantities but on different scales. To normalize these attributes to be on the same scale, I calculate the Z score of each attribute for each observation.

Then, I combine the attributes together of one observation using a weighted average.

For example, if I believe attribute 1 is twice as important as attribute 2, so attribute 1 will have a weight of two and attribute 2 will have a weight of one. I do the same for all observations.

I call the result of the weighted average an “observation Z Score.” I interpret an observation with a Z Score of 1 as being more “exceptional” than 84% of other observations.

Sanity check questions

• Is this method ok?
• Is the method to weight an attribute twice as important with a weight of 2 appropriate for Z Scores?
• Is my interpretation of observation Z Score appropriate?
• What should I do if I have binary data (or other data that is not normally distributed)?

Thanks

submitted by Nevin Manimala Nevin Manimala /u/alexander255110

## How do you know what the “correct” output is for an engine when there’s several different possibly contradictory sources online?

Ages ago, I was researching the 1996 Suzuki Vitara 2.0 V6 / Mazda Proceed Levante 2.0 Long, and noticed several possibly contradictory sources for the power output.

From goo-net-exchange.com:

140ps [107kW] at 6,500 rpm

From parkers.co.uk:

## 134hp

From Wikipedia:

H20A engine

produces 107 kW (136 PS) at 6,500 rpm [isn’t 107kW equivalent to 144hpand 136PS equivalent to 134hp]

From goauto.com.au [source here: