Stupid Questions Thread

Stupid Questions Thread

I'll Begin.

Pic related is the Cayley Table dihedral group of 8 elements (symmetries of a square). This doesn't look like any Cayley table I've ever seen (though I'm new to this sort of math).

It looks as though theyve dropped the header rows and columns, which makes sense as beginning the first rows and columns with the identity makes it clear what the elements are. But what are the red and white little boards above and to the left?

Also, why do we have numbers instead of the typical notation (I've seen r for rotation, s for flip about axis of symmetry, and all sorts of variants of the two, but never numbers)

In fact, there is a lot going on here I'm not familiar with. Can someone help me navigate what is being conveyed here?

Other urls found in this thread:

en.m.wikipedia.org/wiki/Center_(group_theory)
twitter.com/NSFWRedditVideo

>take Physics I at a community college
>realize I am terrible at lab
>Lab worth 30% of grade
>Three test worth 40% of grade
>pre-lecture/lab quizzes worth 10% of grade
>homework worth 10% of grade
>Final exam worth 10% of grade

I just started the class, but assuming I do completely terrible on the lab portion of Physics, can I still pass the Physics class if I average 70% on the test?

Does time actually exist? Or is it just a construct of the mind?

Depends on how terrible is terrible.

Just add up like .7 * .4 for your 70% on the tests, .8 * .1 assuming you get 80% on the quizzes, .9 * .1 assuming you get 90% on the homeworks, etc all the way down except for the labs, then subtract from .7 (or whatever overall percentage you want in the class) and divide by .3 and you have the percentage you need to get on your labs in order to get that grade.

labs, prelecture, and homework having such high percentages are to HELP your grade

As long as you're completing the lab tasks, at least attempting to show a conscious thought process in your lab report, and do the prelectures/homework you should do just fine.

The goal of all that supplementary stuff is to try and make sure everyone is exposed to the concepts/problem solving techniques as much as possible before being tested on it.

Remember that physics, especially fundamental physics, is a model/a conceptual framework for understanding the universe and its processes moreso than a description/some divine elucidation.

A time dimension comes into physical models spanning from fundamental/sub-atomic to standard mechanics to general relativity and greater cosmologies. The notion of time as separate from the spatial dimensions isn't quite right (i.e. Lorentz boosts are fundamental flat spacetime transformations), but it's also a bit off-target to go and say they're the same thing/we live in 4 spatial dimensions (Euclidean time/Wick rotations are useful calculational tricks--even in wacky coordinates the metric signature isn't changed).

Please help

Exams are worth 100 % here, always. It's not good because you cannot make exams comprehensive enough to test everything, so your performance will vary regardless of how well you prepared. This might also people to make it through exams just barely only to utterly fail in many other ones because they estimated the necessary preparation (wrongly) on their previous performance. Furthermore, you might do all your homework (takes much time and also quite some effort) or you might just learn exam questions (takes less time and definity similar or less effort). What do you think is a better strategy to understand your material?

Realistically, with future medical and technological advancement, how long should someone currently in their 20s expect to live?
Are we even close to understanding neural networking to the point of being able to transplant a human brain into say a robot body or a virtual reality? thus achieving a greatly extended life?

Alright I'm starting out with Electronics and can't wrap my head around this problem. I know it's pretty much EE 101 but still would appreciate some help.
I need to calculate the I from this circuit, all the resistances are in Ohms of course. Only the U on R2 is known and it's 15 V.

What I would do is:

Take Rw with R1 as paralell and then add to R2 as serial or something.

>Pic related is the Cayley Table dihedral group
> This doesn't look like any Cayley table I've ever seen
then how the fuck do you know that it is a cayley table?
where did you get it from? what kind of shitsource has a picture like that without a detailed legend to explain the symbols being used?

you might as well ask how to differentiate an upside down questionmark that has a squiggly line beneath it, fucktard

pic related, its a cayley table of the dihedral group of 8 elements. notice the element with the big order, thats the rotation

en.m.wikipedia.org/wiki/Center_(group_theory)

Rw and R1 are not in parallel.
Can you tell when two components are in series or parallel?

Introduce a current I1 in the branch of R1 and I2 in the branch of R2, try to express them.
How does I relate to I1 and I2?

Alright I think I got it now. the I divides into I1 and I2 going to R1 and R2 respectively.
So if U on R2 is equal to 15V then by U = I * R, I1 * 100 = 15 and I2 * 60 = 15.
Then I do I1 + I2 = I and that gives me 0,4 A.

Did I get it right? I assumed the voltage is equal on R1 and R2 since they are paralell.

looks right to me.

Try to keep everything in terms of given values without replacing.
Something like I1 = U/R1, I2=U/R2
I = U*(1/R1 + 1/R2).

This allows you to check for homogeneity in terms of dimensions.
Once you're sure, you can replace with the given values.
Nobody wants to see you write 1 + R + R^2 + ...

wow, you must have a very good understanding of group theory.
For prior to you posting that link to the English wikipedia article on the center of a group, I had no notion of the center of a group, semi-group/noncommutative ring or algebra.

It is only after you posting that link without context that I understand and regret embarassing myself earlier with that post, exhibiting that indeed I was ignorant of what the center of a non-commutative algebraic object with a multiplication was.

However, after educating myself on the matter, one slight little question remains unresolved, and I hope you might shed some light on the matter by elucidating what in the name of FUCK the center of a group has to do with fucking ANYTHING, ever.

Regards, your mother was a whore

Thanks!

That's where I found the image wise ass. You asked where I found the image and how I knew it was the Cayley table of the dihedral group of 8 elements. Now fuck off unless you actually have something to contribute.

How come I can't insert the radius of 6.37x10^6m into the circumference equation of 2rpi then convert the answer to km? my 10^ are a few numbers off. Only way to get the right answer is to first convert the meters to km then plug into the equation.

>How come I can't insert the radius of 6.37x10^6m into the circumference equation of 2rpi then convert the answer to km?
but you can

I did. I did not get the same answer as the back of the book. For part B I get 5.10x10^11km^2 instead of 5.10x10^8km^2.

You will find it is not uncommon for the answers in the back of the book to occasionally be incorrect

I am really dumb so can anybody explain me how did he solve for M in this equation?

The answer on the back of the book is correct if I first convert 6.37x10^6m to km.

Use order of operations and multiply both sides by M to get to the second step, then cube root both sides, isolate M. Its messy but pretty straight forward

you said for the first one.

1km^2 is not 1000m^2, it's 1000 000 m^2.
1km^3 is not 1000m^3, it's 10^9 m^3
this is literally the point of the exercise.

Why can there be no analytic functions with uncountable zeros or poles? I guess an uncountable set of poles would be more of an essential singularity?

so I was suppose to do this? Damn, there was a similar physics lab problem that I had yesterday. Fuck, I am going to do terrible in this class.

Need help with the following exercise.

- Prove a zero-dimensional Noetherian scheme is nonsingular iff it is the union of reduced points.

(Note that the previous exercise was to prove the underlying top. space of every zero-dim. Noetherian scheme is finite, so you can use that.)

I just got admitted to a university. I am taking a class for my major during the summer and I was wondering what would happen if I get an F in the course or a W. Would the university find out and kick me out?

Two are pretty obvious: The dot is the identity, 7 = r^2 (rotating twice)

Since 7 = r^2, it is also pretty obvious that 17 and 22 are either r and r^3; also since they are the only two who have order greater than 2.

Not sure how to find the others, but it should be easy once r and r^3 have been determined. Not sure about the graphs above.

how do I git gud

Physics 1 at a community college? Holy shit, dont fucking do it. Wait till u get to a university to get a real professor vs some dingleberry at highschool part 2

Ow the edge

Best I can come up with is that D4 is a subset of permutations of 4 elements.
The red squares are supposed to be depictions of those permutations.
I don't know why the author of that image decided that permutation of the 1st and 2nd rows and the 3rd and 4th rows correspond to r^2 (or 7 by his notation).

He must have some some method of assigning 0-23 to the 24 permutations of 4 elements.
His method would probably be neat if I knew what he was doing.

Say I know for any [math]\epsilon > 0 [/math] there exists [math]N[/math] such that [math]n \geq N [\math] implies [math]|a_{n+1} -a_n|

What's the difference? My professor has a PhD. The professors who are teaching undergrad Physics at a university are just people with Master's or associate PhD holders who are just doing bitch work for the actual Professor.

Hey, i have no idea wether the following statement is true or false and don't know how to show it, i really need to answer it though and would appreciate your input on this.

The set [math]\{A\in M(n,n)|A*=A\}[/math] of the hermetic matrices is a group in relation to the matrice-addition.
true or false?

I'm not familiar with that set but it's pretty straightforward to show if a given structure is a group: check closure, associativity, presence of an identity element, and closure under inverses. Do you know how to do these things in general?

Alright thanks, i've had groups, sets and so on before and probably learned that but that was 2 years ago and i will have to read into it, I also kind of thought there would be something that i overlooked in that statement that would make the answer seem trivial.

Ah and i did a mistake with the * while writing it. [math]\{A\in M(n,n)|A^*=A\}[/math]

It does not. ln(n) satisfies this but is not Cauchy. The right assumption is that (u_k -u_{k-1}) converge

I meant that the series converge*

How do imaginary exponents work?

with a little bit of imagination.

jk
they don't work.

you can only put an "imaginary exponent" inside an exponential.

if a and b are real,
z = exp(a+ib) = exp(a) * exp(ib).
z has a modulus of exp(a), and an argument b.

Anything else is poor mathematics (including i^i and other shit)

[math] f(x)=3x^2 [/math]
[math] 3a^2=3b^2 [/math]
[math] a^2=b^2 [/math]
[math] a = ±b [/math]
Not one to one
Why does
[math] a^2=b^2 [/math]
come out as
[math] a = ±b [/math]
and not
[math] a = b [/math]?

How to do this if there are two of the same values.

Because a^2=b^2 implies a^2-b^2=(a-b)(a+b)=0 so a=b or a=-b

isn't the same true if you just switch a with b?

so

a=+-b
+-a=+-b

and therefor also

+-a=+-b

???

-a = +-b is the same thing as a = +-b

Then why is it not one to one if -a and +a both = +-b?

Please answer.

I had to solve this problem but couldn't do it on time. I must obtain a relation in which the distance is related to the angle. But I had no idea where to start from the projectile motion formulas.

The answer was supposed to be

[eqn]d(\Theta_0)=\frac{v_0^2sin2\Theta_0}{2g}\left \{1+\sqrt{1+\frac{2gh}{v_0^2sin^2\Theta_0}}\right \}[/eqn]

I guess this would be the best place to ask this.

I have pictures of grains. I want to extract their shape using matlab. The image has quite a bit of noise. After some operations (noise removal, edge selection, bw area open and line dilatation) i get the picture on the right, the grains are pretty much separated but they are still not counted as regions themselves as they are lumps of empty space between small regions.

Any idea on the next step, or a different approach to the problem altogether?

Group the Pi in one side and just go from there.
[math]e=\frac{P_{i}D_{i}}{2f-P_{i}}[/math]
[math]e(2f-P_{i})=P_{i}D_{i}[/math]
[math]2ef-eP_{i}=P_{i}D_{i}[/math]
[math]2ef=P_{i}D_{i}+eP_{i}[/math]
[math]2ef=P_{i}(D_{i}+e)[/math]
[math]\frac{2ef}{D_{i}+e}=P_{i}[/math]

The range is the x distance when y = 0 -- when the projectile hits the ground (there should be two solutions, pick the non-crazy one).

maybe use some hough transformation to detect circles

try morphological opening or closing (can't remember which plugs holes), with a small structuring element.

in your experience, what is the average actual yield for chemical reactions (generally)

and also, what's the closest yield (to a hundred) that you've gotten

100%, strong acid in water

100?, how's that possible, is a rare yield to get?
but what about the average yields?

Depends desu

tell me more

ok, what about precipitationr reactions, what are the average yields then

halp

what does d/dx, dy/dx mean

what would happen if I use acidic water to dissolve sodium carbonate?

d/dx is a differential operator; you applying to a function to get the derivative (of said function).

dy/dx is the derivative of y=f(x). You could also write it as d/dx[y] to show the differential operator is operating in the function y

Uh, you'd get more water?

can being acidic means more H+, right?
but wouldn't the halogens in the air get in there?

I just want to know why its written that way
why d over dx?, does it mean the derivative over the derivative of x
e.g., how do I read it

Read [math]\frac {d}{dx}(f)[/math] as "the derivative of f with respect to "x".

As for why:
1. It's just notation, don't worry about it.
2. Historically, derivatives were thought of as fractions of infinitesimals. [math]\frac {dy}{dx}[/math] was literally a fraction, with dy being the infinitesimal change in y with respect to dx, the infinitesimal change in x.

Perhaps this will help

I don't understand.
if dy/dx means the derivative of y with respect to x, and y = f(x), so that means that you're taking the derivative of f(x), but d / dx means the derivative of f with respect to f, and f = y, whats going on

and sorry, i have to worry about it. I need to know how things work to have a peace of mind

*the derivate of f with respect to x

Surely this is simplistic to answer?

Basically, if y = f(x), we can write the derivative of y/f(x) as:
dy/dx, d/dx(y), or f'(x).
These are all different notation for the same thing.

if y = f(x) then yes, dy/dx means the derivative of y with respect to x.

But d/dx is notation for the differential operator; it is not the derivative of anything. We get a derivative when we apply it to a function (be it expressed as y or f).

As the other user said, the notation is remnant of how derivatives were interpreted way back; dy was an infinitely small change in y, and dx was an infinitely small change in x. The ratio of the two was taken to be the instantaneous rate of change. Its stuck around because, in part, it IS intuitive to think of dy/dx as just that.

I think I get it.
d/dx means the derivative of something with respect to x

so dy/dx means f(x+h) - f(x) / x
e.g. dy == f(x+h) - f(x) and d == x
over smaller quantities to finally be the limit

Sort of, but the d/dx is more of a functional piece of notation than it is anything, sort of like a square root or ln for natural log.

Suppose we have a function y = f(x). It could be anything, a polynomial, logarithm, any of the good stuff you're familiar with from highschool algebra.

Just as we can take the square root of both sides of an equation by literally drawing a radical over the LHS and RHS of the equation, or take the log of both sides by writing log(LHS) = log(RHS), we can apply the differential operator to get the derivative.

so if we have y = x^2 + 2

we can take the derivative (i.e. apply the differential operator) to get

dy/dx = d/dx[x^2 + 2] = 2x

In a rigorous sense an operator is a function that maps a set of functions to itself. I dont know much about that sort of stuff so perhaps another user can help if you want to get deeper.

should say "sort of like a square root symbol" in the very first sentence

I hope this helps and hasn't added further confusion. If you're still stuck just say something an hopefully someone else can explain it better.

It makese perfect sense now.
Are there many properties to derivaties, just like logarithms have properties.

lol oh yes.. numerous

Will I get fucked in my studies of pure math if I skip the probability and statistics module? My program includes them but they are not required, so some of my friends are skipping them and taking pure math classes instead.

PSTAT is HAM AF nigga

what's the best calculator for calculus and beyond?


i know it's not pic related

not interested in that career path at all. I am only asking if I need statistics for pure math somewhere along the line (analysis?)

Veeky Forums help pls

For exams:
Casio 115es plus/991es plus
Casio 991ex classwiz

For homework:
Matlab, Maple, WinPython/Python(x,y) or equivalent

How do I simplify / arrange the result on the left to get something like the result on the right.

Left is just part of the result, but I just want to know how he arranged the square root etc in the book example.

End of first year physics student (UK) going into second year. Any books I should read to prepare? There isn't a course book list for second year yet

I don't know, but it's sure not pic related.

[eqn]\sqrt{\frac{9}{2}}=\frac{3}{2^{\frac{1}{2}}} \Rightarrow \frac{\frac{3}{2}}{\sqrt{\frac{9}{2}}}=\frac{2^{\frac{1}{2}}}{2^{1}}=\frac{1}{\sqrt{2}}[/eqn]

can anyone confirm that these are the masterrace options?

pls no samefag

you guys don't like having the graph display huh? why is that?

Guy with the TI 83 SE here. To be fair, I'm really just trashing it because this model is 17 years old, and I imagine newer ones are more intuitive to use, or have a better display.

Not that I've ever used anything else. Been stuck with this family heirloom since high school.

You won't be allowed to use one in exams and you won't need one outside of them. Save your money.

All you need.

I have 100 trials, in each trial I flip a coin 100 times. This is the same as flipping a coin 10,000 times. What would the distribution of heads and tails most likely look like over all? Say, 50% heads and 50% tails?

most likely yes.

the probability distribution for the number of heads is a binomial distribution with 10000 trials and probability 0.5

And yet if I flip a coin 100 times, I have the same likelihood of getting 100 heads, as I do anything else, like 45 heads and 55 tails.

Please tell me why analytic functions can only have isolated zeros and singularities.