/sci/ - Science & Math » Thread #13721414

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Test, not Homework

Anonymous Wed 06 Oct 08:56:08 2021 No.13721414 View Reply Original Report

Quoted By: >>13721420 >>13721561 >>13723309 >>13723361 >>13723518 >>13723854

I asked a legitimate question: How could I have solved this Test Question, which I could not do.
I received a "Warning" from a Mod for doing so.
I clearly indicated it was not homework, yet was accused of posting homework.
Why?

Anonymous

Anonymous Wed 06 Oct 2021 08:58:34 No.13721419 Report

Quoted By: >>13721425 >>13723298 >>13724218

DO NOT REPLY THIS DERANGED POSTER IS GOING TO MISS OUT ON POINTS FOR BEING A BRAINLET AND GETTING FILTERED BY HOMEWORK

Anonymous

Anonymous Wed 06 Oct 2021 08:58:37 No.13721420 Report

Quoted By: >>13721422 >>13721747

>>13721414
>Why?
It's because you used x as both the bound variable and the free variable

Anonymous

Anonymous Wed 06 Oct 2021 08:58:53 No.13721421 Report

Quoted By:

>>13721295

Anonymous

Anonymous Wed 06 Oct 2021 08:59:55 No.13721422 Report

Quoted By: >>13721427 >>13721429

>>13721420
>you used x
No, this is the problem as given on the Test.

Anonymous

Anonymous Wed 06 Oct 2021 09:00:56 No.13721425 Report

Quoted By:

>>13721419
please fuck off, Cadet Capslock

Anonymous

Anonymous Wed 06 Oct 2021 09:01:45 No.13721427 Report

Quoted By: >>13721431

>>13721422
That's too bad. Now no one will ever know what the question means

Anonymous

Anonymous Wed 06 Oct 2021 09:03:11 No.13721429 Report

Quoted By: >>13721436

>>13721422
Not him but something is weird here.
.H5 would be integral of (.…..) d5

Anonymous

Anonymous Wed 06 Oct 2021 09:04:24 No.13721431 Report

Quoted By:

>>13721427
>Now no one will ever know
In my course, the Professor is not clear on a lot of things.
I don't take that as an excuse not to know them.

Anonymous

View Same Google iqdb SauceNAO H_5.png, 6KiB, 640x320

Anonymous Wed 06 Oct 2021 09:12:03 No.13721436 Report

Quoted By: >>13721533 >>13723470 >>13725313

>>13721429
Here is something that I thought of tonight.
Substitute _5_ for _x_ in the original formula, and solve for the constant of integration.
Would this be a legitimate approach?

Anonymous

Anonymous Wed 06 Oct 2021 09:35:16 No.13721479 Report

Quoted By: >>13721506 >>13723466

The integration variable is not the same as the input for H; those are two different things. Moreover, that's an indefinite integral, so the antiderivative will have a +C. Whoever wrote the question is an idiot, because this makes no sense.

Anonymous

Anonymous Wed 06 Oct 2021 09:47:31 No.13721506 Report

Quoted By:

>>13721479
>Whoever wrote the question is an idiot
In our course, the Professor is unengaged,
and borrows a lot of material from online sources.
I will attempt to ask him for clarification Thursday.

Anonymous

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Anonymous Wed 06 Oct 2021 09:55:53 No.13721533 Report

Quoted By: >>13721596 >>13721603 >>13721620 >>13723414 >>13723470

>>13721436
Here is my procedure to evaluate H(2)
...is this reasonable, or am I delirious?

Anonymous

Anonymous Wed 06 Oct 2021 10:06:08 No.13721561 Report

Quoted By: >>13721567 >>13721620 >>13721747 >>13723628

>>13721414
$H(2)=\pi-\int_2^5\frac{x^3-sinx}{x^2+2}dx$

Anonymous

Anonymous Wed 06 Oct 2021 10:08:12 No.13721567 Report

Quoted By:

>>13721561
Yes, that looks correct, but how do we evaluate it?

Anonymous

Anonymous Wed 06 Oct 2021 10:19:43 No.13721596 Report

Quoted By: >>13721608

>>13721533
it should be -cos(2) and -cos(5), not sine.

Anonymous

Anonymous Wed 06 Oct 2021 10:21:30 No.13721603 Report

Quoted By: >>13721612

>>13721533
>or am I delirious?
Yes, this problem makes no sense. Just ask your professor what the bounds on the integral should be instead

Anonymous

Anonymous Wed 06 Oct 2021 10:22:22 No.13721608 Report

Quoted By:

>>13721596
>it should be -cos(2) and -cos(5), not sine
wat

Anonymous

Anonymous Wed 06 Oct 2021 10:26:02 No.13721612 Report

Quoted By:

>>13721603
>ask your professor what the bounds on the integral should be
I shall attempt that, but he is very uncommunicative.
He will answer a question with "What do you think it is?"
As though we should somehow know.

Anonymous

Anonymous Wed 06 Oct 2021 10:28:28 No.13721620 Report

Quoted By: >>13721651 >>13723477

>>13721533
Cant be sure i mean IT could be right but there is no telling from the input given.
I too thought initially about something more about the lines of>>13721561
That would mean that orig question is should have upper limit of integraton as x, lower as whatever ( H(2) shares it , IT would be constant for any x) and the solution is obtained by substracting the common part. But again variable under integral should be different than x.
To proceed just solve the integral from5 to 2

Anonymous

Anonymous Wed 06 Oct 2021 10:38:58 No.13721651 Report

Quoted By: >>13723091

>>13721620
>solve the integral from5 to 2
That is the problem, I couldn't.
Wat do?

Anonymous

Anonymous Wed 06 Oct 2021 10:42:38 No.13721659 Report

Quoted By: >>13721673

Dumb little kiddies

Anonymous

Anonymous Wed 06 Oct 2021 10:47:24 No.13721673 Report

Quoted By:

>>13721659
fuck off, Grandpa

Anonymous

Anonymous Wed 06 Oct 2021 11:22:09 No.13721747 Report

Quoted By: >>13722997

>>13721420
hilarious that /sci/ has forgotten what an indefinite integral is.
>>13721561 is about the simplest form you can get it to, the integral of sin(x)/(x^2+2) doesn't have a nice form except over the whole real line

Anonymous

Anonymous Wed 06 Oct 2021 20:41:23 No.13722997 Report

Quoted By: >>13723113

>>13721747
Indefinite integrals don't give you a function, dumbfuck; they give you a family of functions. The output at any x could literally be anything, and it depends on the +C which you seem to have forgotten.
>b-but they gave you that H(5) = pi
Which is fucking useless, because this indefinite integral doesn't have a closed form in terms of elementary functions, so you can't possibly know what H(2) is.

Anonymous

Anonymous Wed 06 Oct 2021 21:29:47 No.13723091 Report

Quoted By: >>13723477

>>13721651
Well you got me curious and i tried to split it to arctan and sine on u v decomposition to check if it cycles back to original expression but eventually signs do not match up and you end with 0=0.
Its either something requiring nonstandard approach or just nonsense problem. What is the overall level of the course? More basics or something after your first analysis (which i doubt)?

Anonymous

Anonymous Wed 06 Oct 2021 21:41:44 No.13723113 Report

Quoted By:

>>13722997
>you can't possibly know what H(2) is
Obviously H(2) is just the definite integral from 5 to 2 plus the constant ?.
The fact that you have a hard time computing it doesn't mean that it isn't precisely determined.

Anonymous

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Anonymous Wed 06 Oct 2021 22:50:46 No.13723274 Report

Quoted By: >>13723277 >>13723313 >>13723414 >>13723628

The problem, as written, makes no sense. It doesn't matter that it's a definite integral. If your professor really gave you this problem then... good luck, lol

Anonymous

Anonymous Wed 06 Oct 2021 22:51:48 No.13723277 Report

Quoted By:

>>13723274
indefinite*

Anonymous

Anonymous Wed 06 Oct 2021 23:02:30 No.13723298 Report

Quoted By:

>>13721419
I never did math homework, I just turned in my scratch paper that I practiced for tests with and the grader had to figure out if any of the practice problems matched up.

Anonymous

Anonymous Wed 06 Oct 2021 23:09:22 No.13723309 Report

Quoted By:

>>13721414
The question would be easy if the antiderivative was simpler.

1. Integrate
2. Insert x = 5 and pi, and find constant C
3. Calculate H(2)

Anonymous

Anonymous Wed 06 Oct 2021 23:10:12 No.13723313 Report

Quoted By:

>>13723274
What makes you say that it makes no sense?
Is it because the integration variable is the same as the function parameter for H?
Or is it because of the fact that H is only defined to within a constant?
Why would either of those present a problem even to a beginner student?

Anonymous

Anonymous Wed 06 Oct 2021 23:28:37 No.13723361 Report

Quoted By: >>13723657

>>13721414
>I received a "Warning" from a Mod for doing so.
Did you actually think math and physics were allowed here? I got banned for posting a chart of 30 years of gambling data to evaluate the gambler's fallacy as "off topic". This board is /pol/lite and that's all it is.

Anonymous

Anonymous Wed 06 Oct 2021 23:52:20 No.13723414 Report

Quoted By: >>13726456

>>13721533
>>13723274
are you retarded or autistic?

Anonymous

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Anonymous Thu 07 Oct 2021 00:19:02 No.13723466 Report

Quoted By:

>>13721479
>brainlet can’t into calc I FTC problems
Filtered. >>>/g/

Anonymous

Anonymous Thu 07 Oct 2021 00:20:09 No.13723470 Report

Quoted By:

>>13721533
>>13721436
Yep, this is the only way of looking at the problem that makes any sense. It's a very weird question though.

Anonymous

Anonymous Thu 07 Oct 2021 00:22:47 No.13723477 Report

Quoted By: >>13726493

>>13723091
>>13721620
here is the solution if you're curious:
https://www.wolframalpha.com/input/?i=integrate+%28x%5E3+%2B+sin%28x%29%29%2F%28x%5E2+%2B+2%29

Anonymous

Anonymous Thu 07 Oct 2021 00:41:08 No.13723518 Report

Quoted By:

>>13721414
What is the type of function H?
H : R -> (R -> R)
Why? Well, the vairable x as an argument of H is shadowed by the x under the integral sign.

We have:
(1) H(x) = (t |--> A(t) + C), where A(t) is the antiderivative and C some constant.

(2) H(5) = Pi

From (1) and (2) we see that:
H(5) = (t |--> A(t) + C) ==> Pi = (t |--> A(t) + C)

Even if we treat Pi as a constnat fucnton (t |--> Pi), we still get the contradiction (from (1) and (2)):

(t |--> A(t) + C) =/= (t |--> Pi)
(we cannot find such constant C so this will "work out").

(Also mods for /sci/ can even tell what is a homework and what is not, shame.)

Anonymous

Anonymous Thu 07 Oct 2021 01:39:14 No.13723628 Report

Quoted By:

>>13723274
The problem makes "sense"
The issue is the indefinite integral is nasty so you're not going to find it analytically.

You could do>>13721561
And solve it numerically. Without context for the type of class it's hard to say if this is expected or even doable, especially if it's an exam.

Anonymous

Anonymous Thu 07 Oct 2021 01:59:04 No.13723657 Report

Quoted By:

>>13723361
Based gambling shill

Anonymous

Anonymous Thu 07 Oct 2021 03:28:11 No.13723854 Report

Quoted By: >>13726498

>>13721414
It’s 2pie/5, are you dumb?

Anonymous

Anonymous Thu 07 Oct 2021 07:32:57 No.13724218 Report

Quoted By:

>>13721419
fpbp

Anonymous

Anonymous Thu 07 Oct 2021 13:54:49 No.13724971 Report

Quoted By:

what the fuck does the integral end up being a constant? How is that possible...
I'd just say that H(2) = pi in that case

Anonymous

Anonymous Thu 07 Oct 2021 14:29:29 No.13725083 Report

Quoted By: >>13726515

I plugged the integral into planetcalc.com and got the answer H(2) = ?5.86666 to 6-digit accuracy.
Maybe OP was asked to compute by using numerical integration, e.g. Simpson's method.

Anonymous

Anonymous Thu 07 Oct 2021 15:33:32 No.13725249 Report

Quoted By:

>getting filtered by a trivial single variable integral
the absolute state of /sci/

Anonymous

Anonymous Thu 07 Oct 2021 15:55:25 No.13725313 Report

Quoted By: >>13726523

>>13721436
This looks right to me, the reason this problem is so fucking stupid though is under exam pressure you'd assume you need to solve the initial integral which would be nearly impossible under exam time limits. Unless you saw a problem like this in class or on homework, it's just a dick move

Anonymous

Anonymous Thu 07 Oct 2021 20:40:52 No.13726456 Report

Quoted By:

>>13723414
autistic, maybe; but not retarded.
you?

Anonymous

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Anonymous Thu 07 Oct 2021 20:51:17 No.13726493 Report

Quoted By:

>>13723477
yiiikes

Anonymous

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Anonymous Thu 07 Oct 2021 20:52:42 No.13726498 Report

Quoted By:

>>13723854

Anonymous

Anonymous Thu 07 Oct 2021 20:56:38 No.13726515 Report

Quoted By:

>>13725083
D'oh!

Anonymous

Anonymous Thu 07 Oct 2021 20:57:48 No.13726523 Report

Quoted By:

>>13725313
thx Anon
Test was one hour, eight problems, postponed from last week.
This was Problem 7, the hardest of the lot (for me) -- and Problem 8 was easy.
We'll get our grades on Tuesday.

Anonymous

Anonymous Fri 08 Oct 2021 04:56:17 No.13727882 Report

Quoted By:

Try ln(5^2+1)+sin(5^2)+.0158478656. Use Taylor series of int[(arctan(x))’x^3dx] + int[(arctan(x))’sin(x)dx] to get the approximation to pi. Idk if it's right, but that's my attempt.

Anonymous

Anonymous Fri 08 Oct 2021 05:29:17 No.13727951 Report

Quoted By:

Today our Professor said he would explain it Tuesday.
We'll see.

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