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/sci/ - Science & Math

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7120985 No.7120985 [Reply] [Original]

Is this legal or am I complete fucking piece of useless shit?

>> No.7120993

>>7120985
perfectly legal.

>> No.7120995

>>7120985
why would it not?

>> No.7120996

>>7120985
that is legal you are piece of shit

>> No.7120997

It can be two things.

>> No.7121009

As legal as a supple 14-year-old in Canada circa 2000.

>> No.7121014

No, you have to do the quotient rule inside the product rule

>> No.7121050

>>7120985
You are clearly integrating with respect to x' in a probability space so the answer is x^3/x.

>> No.7121135

+ C

>> No.7121148

>>7120993
>>7120995
>>7120996
>>7121009
Ignore these trolls. I almost got arrested for doing the same thing on a test.

>> No.7121184
File: 39 KB, 600x196, 1424044694775.jpg [View same] [iqdb] [saucenao] [google]
7121184

>> No.7121189

>>7120985
>no differential

2/10 made me reply

>> No.7121197

>>7120985

Why not just reduce it from the beginning where x^3/x = x^2 then integrate. You're just doing an extra step.

>> No.7121213

>>7121189
differentiate these nuts from ya face boi

>> No.7121254

>>7120985
Yes, it's perfectly legal because though in a sense (in a natural domain sense) those two functions are different, integrating over them is the same (that 0 point doesn't make any difference to the integral).

>> No.7121269

>>7120985
>not using trigonometric substitution

top kek

>> No.7121284

>>7120985
Where that +C at??

>> No.7121292

RESPECT TO WHAT?
AND WHERE'S YOUR CONSTANT OF INTEGRATION?
KILL YOURSELF

>> No.7121302

>>7120985
you just canceled an x

if it was legal in 6th grade, it still is now

also, no dx, C, etc... where your mind at child?

>> No.7121518

>>7121135
/thread

>> No.7121532

>>7120985
Are you talking about x being in the complex plain? If so this is not entirely legal. Using logarthmic subsitution.

>> No.7121571

>>7120985
Fuck the trolls. It's not legal. The problem is, on your case it's working. But not everytime.

>> No.7121613

>>7121292
Often times in pure maths we leave the constant off (provided it is not necessary for what follows) because it's obvious and everyone know it's there.

It's a very school childish thing to get pissed about that.

The fact op doesn't know what he's doing at all and those statements are nonsense is a separate matter entirely though...

>> No.7121614
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7121614

it's not legals since you don't know this!!!

>> No.7121627

>>7120985
What are you integrating with respect to?

>> No.7121662

>>7121189
This.

>> No.7121667

>>7120985
depends on who will read your paper?
if a physicist, engineer or anyone who uses math for a purposes reads it, he will consider it correct.
a mathematician could, i donno about mathematicians
if you need the answer to that integral for something you are going to "use" in real life, it is absolutely a correct way to do it

>> No.7121672

>>7121667
>If it's an engineer it doesn't matter, just suck his dick
>>7120985
No dx, no +c other than that it's ok

>> No.7121686

>>7120985
hey bro what variable are you integrating with respect to

>> No.7121812

>>7121292
>>7121627
>>7121686
itt: smartasses

>> No.7121819

Someone report this faggot for not including a dx, I'm on mobile

>> No.7121851

>>7121197
because it's not the same for x=0.

>> No.7121853

>>7121851
this is what mathematicians actually think

>> No.7121887

>>7121009
Canadian here.

https://www.youtube.com/watch?v=-9JOmU2jFUo

>> No.7121889

>>7121887
Whoops. wrong song.
https://www.youtube.com/watch?v=gs58_ZvsbBI

>> No.7121927

>>7121853
They think so because it's right.

If op clarifies that x=/=0 everything should be working well.

>> No.7121971

>>7121927
But {0} is a zero measure set...

>> No.7121979

>>7121971
your dick is a measure zero set

>> No.7122000

>>7121927
It's fine for x=0 too because it's a Lebesgue null set.

>> No.7122026
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7122026

Totally legal

>> No.7122096

>>7121184
kek

>> No.7122315

>>7121148

Best reply.

>> No.7122320

How else is this supposed to be integrated?
Clearly the answer IS x^3/3, how do you suggest we reach that answer?

fulltime cocksucker, engineering hobbyist

>> No.7122351

>>7121135
Underage ban

>> No.7122366

f(x)=(x+1)sin(3x)

Can anyone please explain to me why the graph of this function will lie below the x axis for values of x in the interval [4pi/9,5pi/9]?

>> No.7122380
File: 2.68 MB, 220x280, 1425974443734.gif [View same] [iqdb] [saucenao] [google]
7122380

>>7122366
sin (3X)
x=4pi/9
>>>
sin(3*4pi/9)=sin(12pi/9)=sin(pi + 3pi/9)
and on the unit circle that comes below the x axis so the sin is negative.

>> No.7122404

>>7122380
Thanks!

>> No.7122426

>>7121269
There is literally no such thing as trigonometric substitution. I think you mean INVERSE, trig substitution, niggershitter

>> No.7122430

>>7122426
x=tanu???

>> No.7122437

>>7122430
You can only substitute if it has a unique inverse

top kek faggot, go bak to high school

>> No.7122468

>>7122437
what are you talking about...
how do you integrate
1/sqrt(1+x^2)dx

>> No.7122476

>>7122468
arcsin(x/sqrt(1))

>> No.7122477

>>7122476
my bad, that is ln(x+sqrt(1+x^2))

>> No.7122493

>>7122476
>>7122477
this has to be a troll, no one integrates that way

>> No.7122495

>>7122476
>>7122477
>>7122493
that is the ANSWER of the integral, my question is how do you get there
u=tanx, will get you there

>> No.7122535
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7122535

>>7122495

>> No.7122543

>>7122535
using formula:

integral of 1/(sqrt(u^2 +/- a^2)

=

ln(u+sqrt(u^2 +/- a^2)

>> No.7122563
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7122563

>>7122535
fite me

>> No.7122586

>>7122563
my methods definitely better. you had to draw a triangle, faggot. also, who wants to deal with sec?

>> No.7122593

>>7122563
Also, as i have been saying, this is not a legitimate substitution because it does not have a unique inverse function (a criterion for substitution). Your arrival at a solution isnt proof that trig sub is valid

>> No.7122603

>>7122593
oh yea?
i beg to differ
https://en.wikipedia.org/wiki/Inverse_trigonometric_functions#Principal_values

>> No.7122609

>>7122603
>https://en.wikipedia.org/wiki/Inverse_trigonometric_functions#Principal_values

Did you use arctan? no, you didn't faggot. Arctan has a unique inverse function but tan does not

>> No.7122614

>>7122609
i have done tanu substitutions all my life, it always works
thinking that it might fails, means you do not understand integrals

>> No.7122623

>>7122614
I didn't say it would fail, i said it's not valid or substantiated in theory. It's mathematically "illegal."

And even it it wasn't, my demonstrated method IS better

>> No.7122639

>>7122623
>I didn't say it would fail, i said it's not valid or substantiated in theory. It's mathematically "illegal."
none of my engineering teachers (u mad yet?) cared about that, so, i repeat, fite me
>>7122623
>my demonstrated method IS better
i must admit, for someone who does not know trigonometric identities, your method really is simpler
however my method involves less algebra, polinomials and whatnot
also you have not obtained the final result, in terms of x
getting to the final answer using a triangle, is a shorter step

>> No.7122650

>>7122639
Nigga, I obtained the final result without ANY work in >>7122477
I did the problem in my head using >>7122543

I just wrote it out because you asked how to get there and it's not immediately clear (and sometimes you need to algebraically manipulate it a little into the formula)

Also, I am an engineering student, not a math nerd