/sqt/ - Stupid Questions Thread

Yes, I graduate with a BSEE in December this year and have had some research experience in both fields. My adviser has said my stats are good enough to get into top programs as well, based on past students from my uni.

So im supposed to find relative min max and saddle points if any in the pic related function.
I got fx=2x and fy=1-e^y
at this point usually we do a system to find the critical points so at which points both fx and fy are 0 but neither of them have 2 variables so i cant really solve the system.
what do next?
should i just say no critical points and not use the second partial test at all?

nvm im retarded
no need for system at all

>neither of them have 2 variables so i cant really solve the system.
yes you can, for example if fx=2x=0 then x=0 and y= anything

How do I solve this?
x goes out as a constant then what?

substitute u = xy^2
du = 2xy dy

(when you do a substitution like this, when you find du you're taking derivatives with respect to the same variable the integral is with respect to, in this case y)

what does this notation mean

it's a "second order partial derivative". You take the derivative of f with respect to x_j, and then take the derivative of that with respect to x_i.

The second order partial derivative derivative of f, first taken with respect to x_j, then with respect to x_i.

i still dont quite get it
ehhhhhhhh im retarded

[eqn]\int xy e^{xy^2} dy[/eqn]
[eqn]u = xy^2[/eqn]
[eqn]\frac{du}{dy} = 2xy[/eqn]
[eqn]du = 2xy \;dy[/eqn]
[eqn]\int xy e^{xy^2} dy = \int \frac 12 e^u du[/eqn]

I dont understand the last part whats that 1/2 and where did xy go

xydy gets replaced with 1/2 du cuz they same

I see
thanks

Question about extrapolation and crime reports

Is it really true they used a sample size of 10 white women to claim there are 16k black on white rapes?
businessinsider.com/stupid-racist-meme-rape-black-men-2016-10

Here's the report
bjs.gov/content/pub/pdf/cvus08.pdf

woah... really made me tink
thanks fampai

should i replace u back after removing the intergral sign or just calculate the value of the definite integral directly

integral-calculator.com/

>a BC CS

into the trash.

I have a really stupid question. I just need you to check my procedure and tell me at what step I made a mistake.

Suppose that [eqn] \lim_{x\to\infty} \frac{f(x)}{g(x)} = 1[/eqn]

Then

[eqn] \lim_{x\to\infty} f(x) - g(x) = \lim_{x\to\infty} (f(x) - g(x)) \frac{g(x)}{g(x)} = \lim_{x\to\infty} \left(\frac{f(x) - g(x)}{g(x)}\right) g(x) = \\ \lim_{x\to\infty} \left( \frac{f(x)}{g(x)} - \frac{g(x)}{g(x)} \right)g(x) = \lim_{x\to\infty} (1 - 1)g(x) = \lim_{x\to\infty} 0g(x) = 0 [/eqn]

It looks just fine to me. Maybe I'm retarded though

No, it has to be wrong. For example consider f(x) = x^2 + x, g(x) = x^2 + 2x

The limit of their quotient is 1 but their difference diverges.

But it looks almost true, but somewhere there is something wrong.

[math]\omega_0dz_1/d\tau -z_1 = \rho_0^4e^(4i\tau) -i\omega_1\rho_0e^(i\tau)[/math]

If i wanted to try a particular solutions for this would i try [math]z_1 = Pe^(i\tau)+Qe^(4i\tau )[/math] or [math]z_1 = P\tau e^(i\tau) + Qe^(4i\tau)[/math]

I assumed it would be the latter because [math]Pe^(i\tau)[/math] is in the homogenous solution. i don't know how to get the exponential powers right

There's a mistake in the last but one equality where you suddenly claimed that f/g = 1, which is not true, because only their unbounded limit is equal to one. You're using arithmetic of limits without verifying the assumptions first. First you would have to assume that the limit of g(x) exists and limit of f/g - g/g exists and their product doesn't have indetermine form, then you have to use arithmetic of limits one more time while checking that the limit of f/g - g/g exists and has a meaningful value (non-intedermine form).

To add to that: by using your example of f and g, we have that g has the limit equal to infinity so we get the indeterminate form (assuming g/g = 1)

[math] \lim_{x \to \infty} \Big(\frac{f(x)}{g(x)} - 1\Big)g(x) = 0\cdot\infty [/math]

Id replace u back.

are you trying for undetermined coefficients? why? it's first order, just use the general method for first order linear equations. and if you insist on using undetermined coefficients the first guess for the particular solution is right.

What is the minimum amount of moves it takes to move a tower of Hanoi n layers tall from one peg to another?

oh yeah, there are 4 pegs instead of 3.

I know that 3 pegs is

[math]2^n - 1[/math]
or
[math]T_0 = 0,[/math]
[math]T_n = 2T_{n-1} + 1[/math]

Can you request books for someone to upload to Library Genesis?

Is the biological species concept the most applicable way to define species? If so, at what point does a species diverge into two in the context of the differences between their genomes? Is there a specific locus or chromosome in which this reproductive isolation is accelerated?

Hello friends

I need to take the general GRE for a fellowship and grad school applications. I've taken some practice tests and they seem pretty trivial.

Is the real exam more difficult? Should I bother preparing or is it really that easy?

Recommended books for undergrad Physical Chemistry? How's Atkins?

the math section is like what you'd expect an 8th grader to be able to do. The only obstacle is the time limit, and not making little mistakes and falling for one of the trap answers.

Atkins or McQuarrie & Simon.

M&S may be a bit dated but it's a stupid good intro to PChem. One of my favorite texts.

McQuarrie and Simon's approach (quantum mechanics first) is extremely interesting but that's not how the course is going to be structured.

Depends on your practice test. The material won't really go past lower-level maths like algebra and geometry. However, the exam is written to be tricky, and the time is a hhhhuuuuuge constraint. Keep in mind that in the actual test setting, you will take 4-5 30 minute exams with very few breaks.

Lets say I'm playing a game. In this game there are 5 valuse that each can range from -40 to +40. I can "roll" and all 5 values will randomly assign themselves between -40 and 40. This count as one roll. Each roll is independent and does not affect the outcome of another roll. There are two people, one will roll 100 times and the other will roll 1000. My question is would rolling more times up the probability of getting the positive outcome were all values have 40 or will the probability stay the same for each roll because each roll is random and idependent of the other?

What kind of mathematics do you use in mechanism design besides geometrical things?
What branches of mathematics should i study if i liked discrete maths

Anyone knows a good database with charts of applications vs accepted applications for various universities over time? I'm looking into really old stuff, at least 1990s old.

I'm having a lot of trouble solving basic systems of equations using Gaussian elimination. Does anyone have any insight or tips ?

Practice more, be careful, don't skip steps.

>Is the biological species concept the most applicable way to define species?
It's the concept that's used the most but definitely not the one everybody adheres to.

>at what point does a species diverge into two in the context of the differences between their genomes?
That's not the biological species concept. You're talking about the genetic species concept now. Here's a paper on it.
mammalsociety.org/uploads/Baker and Bradley 2006.pdf

I flip a coin once and look at the result. You flip a coin a million times and look at the result of the final flip. Who has the higher chance of getting heads? The rolls are independent events so the chances don't change.

what direction should I do the steps?

applied electromagnetics/RF circuits vs optics/photonics for EE grad school?

Is there any reason not to early apply if I know *that* is the college I want to get into?

Do it if you really want but undergrad uni is a meme and it is best to choose the best, "cheap" college you get into. Friend is $130k in debt from MIT undergrad while I am only $2k from best school in my dinky state. We both are in the same PhD program now at a highly ranked EE uni.

Has under/BS programs always been like this? Like, take the 90s or early 2000s for example. Were those degrees as worthless then? Just wondering, genuinely curious.

I think the article is weak. The stuff about raping spouses and prisoners is, frankly, bizarre. And I' sure nobody really thinks white men "never" rape block women.

And what does "disproportionately " mean here?

Im not sure I did not attend in those times. Got BSEE in 2015 and now on 3rd year of PhD. BS degree is not worthless, it is just that the place you get it generally doesnt matter that much in STEM if you do well anyways. Especially if you only get a bachelors and then a job, the uni you attended will not matter after your first year of real job experience. It matters a little for grad school as having professors that attended top schools as references and joining their research can be nice, but there is always summer research at outside universities.

this makes no sense, how can the vector which is 2/3 of v be made by adding 2/3v to v? shouldn't 2/3 v be the answer?

because you aren't doing that,
you are finding the vector v between points a and b
then adding 2/3 of vector v to point a, to find a point 2/3 the way between them
you are NOT adding 2/3 v to v, as you suggesting, and the answer is NOT 2/3 v
2/3 v is what you have to add to the initial point a

so 2/3v is just a point 2/3 from the origin that's collinear to a? sorry im and idiot.

Your question seemed a bit unclear to me, but if you are asking about the probability that the person — at least once — got a role of all forties, then the probability is different between both players. The player rolling 1000 times has a higher chance of getting a role of all forties at least once. But as already noted, the distribution of values of all their roles takes the same "shape"

When they say "the vector for the first point" they don't mean v they mean the first point, so if the two points are a and b, then v is b - a, and the answer is a + 2/3v not v + 2/3v

how do i integrate a variable with a -1 exponent? after integrating it becomes 0 so what do i do from there?

>after integrating it becomes 0
no, power rule only works for powers that aren't -1

int x^{-1} = log x

for combinatorics, you can say something like "5 choose 3" to represent having 5 objects and wanting to know how many combinations exist when you take 3 of these objects out and order of the objects does not matter

is there a similar "spoken" type of phrasing this for permutations? Ive never done anything combinatoric related and I have no idea how to phrase that for google

i don't think it's standard but you could say 5 choose 5 without replacement

What kind of questions am I allowed to ask?

How much time do you all spend on average on exercise problems when reading for fun?

I don't have a lot of time to read for fun so if an answer doesn't come to me within 5-10 min I usually just look for an answer somewhere.

I usually do this for topics that are not particularly relevant to what I am studying at university, but that I still have some interest in.

I have no clue how to answer question 99. Sorry for the flipped image, stupid phone app always flips images

Haven't you learned how to solve systems of linear equations in high school? You are doing exactly the same thing.

I am working with powder processing. Is there a word that designates the act of reducing bulk solids into powder? Milling/grinding seems to be the preferred terms e.g. ball milling.

I'm looking for a way to cheaply produce powder samples with reproducible size distribution.

Try working backwards. Given that [math]\log_4 p = 0[/math] what can we deduce about p?

>what can we deduce about p?
It is the 16th letter in the alphabet

Rules to remember:
loga(a) = 1
loga(1) = 0

log2[log3(log4x)] = 0

For log2 to be 0, log2(1) is required
log3(log4x) = 1
for log3 to be 1, log3(3) is required
log4(x) = 3
x = 4^3
x = 64

log3[log2(log4y)] = 0
"
log2(log4y) = 0
"
log4y = 2
4^2 = y
y = 16

log4[log3(log2z)] = 0
"
log3(log2z) = 1
"
log2z = 3
2^3 = z
z = 9

x + y + z = 64 + 16 + 9 = 89

Logic question I been wondering about

Do you ever want to use an implication if you have just an existential somewhere in your logical formula?

For instance Let E represent "There Exist"

Ex(P(x) -> Q(x) is that fine?

Ex(P(x)->Q(x)) is that fine?

In either situation if P(x) is false then the entire formula is true.

Is that what you really want?

What or where would one find a good source for solving confusion matrices?

I have a list of problems to solve, where I have to solve for the two remaining blank matrix spots, and am having a hard time understanding where to begin.

All help is appreciated, thank you.

Have there been any occurrences of say, shitty scientists from the 1800s who don't know what they're doing (due to lack of technological advancement), trying to figure something out, ruin it, and now modern scientists can't test on it because of the old idiots? Thinking along the lines of paleontology or geology. But anything really.

x is treated as a constant, do a u substitution with y^2 as your u. the dy/du will allow you to include the only other y in the equation, then you sub in everything and do the integral, then plug back in

[math]\exists x(P(x) \rightarrow Q(x))[/math]
Says, there exists something such that if that thing is P, then it is Q. Therefore this statement is true in any non-empty universe except the universe which contains only things that are P and not Q. It's a very weak statement which is why conjunctions usually go with existentials, but I suppose you may be able to come up with an example where it's illustrative.

Not sure about scientists, per se, but recent man-caused extinctions could have been better handled. Passenger pigeon, thylacine, dodo, who-knows-what-on the Galapagos Island burned for fun. How big did whales get before we killed the big ones?

You could say the idiots that screwed up Three Mile Island and Chernobyl fucked away our best chances at petroleum independence.

Don't forget Fukushima, that scared the German people into shutting down its plants and becoming dependent on Russia.
I still don't eat fish, there'a apparently loads of cesium going into the Pacific right now.

Schliemann destroyed a lot of Troy VII looking for Homeric Troy, which he took to be Troy II.
It's also disappointing to me that Mendel and Darwin never met.

how do you pronounce the words "german" and "germany" in english? "germ"an? yerman?

Bump.

FOR EVERYBODY WHO'S TIRED OF RETARDS AND AUTISTS IN THIS THREAD, OF LAZY COCKSUCKERS NOT EVEN TRYING AND OF UNEDUCATED SCUM NOT ANSWERING ANY FUCKING QUESTIONS BEYOND HIGH SCHOOL LEVEL:

ASK YOUR QUESTIONS HERE:
No need to try to make work something that clearly isn't fucking designed to work.

If this OP has to bump his thread and shit up my own with his bullshit falseflagging, that's how you know he should GTFO from sci.

What the fuck is wrong with you?

The first one. The g sounds the same as in "giraffe" and "gentle"

Imagine being this guy.

How many meds do you think he forgot to take this morning?

Why are you like this?

I am studying point set topology for the first time and I don't get what is so complicated about (3).
I am under the impression that it's an immediate consequence of the definitions.
Am I overlooking something ?

>I am under the impression that it's an immediate consequence of the definitions.
Try to make a clear argument in mathematical language then

V is the inverse image of U by the inverse of f wich is continuous
U is open hence V is open

with f : U -> V homeomorphism

i'm no expert but your map f is from U to V, so I think it only tells you V is open in the subspace topology induced by R^n, not in R^n itself

anyway it's this theorem:
en.wikipedia.org/wiki/Invariance_of_domain

thank you

PKA has four regulatory subunit isoforms: RI alpha, RI beta, RII alpha, RII beta. The difference between RI and RII is a single phosphosite (alanine to serine). RI works as pseudosubstrate, RII works as real substrate, both inhibit PKA activity. Why does RII stay in the binding pocket after phosphorylation of serine?

Might be a bit specific. Maybe someone can answer

Nice try OP. Except everybody has caught up to your samefagging by now.