integration (1 Viewer)

shuning · Apr 29, 2009

回复: Re: 回复: Re: integration

GUSSSSSSSSSSSSS said:
lol greaaaaaaaaat question shuning =P

but actually quite a few people in australia write it the way drongoski did xD
...even my bogan math teacher

for example today he gave us a math joke:

FIND:
integral(1/cabin)d(cabin) .... xDD

no no no... i mean actually drag stuff into the dx bits and work on it LOL

btw i dont get teh joke ...

Drongoski · Apr 29, 2009

Re: 回复: Re: integration

GUSSSSSSSSSSSSS said:
lol greaaaaaaaaat question shuning =P

but actually quite a few people in australia write it the way drongoski did xD
...even my bogan math teacher

for example today he gave us a math joke:

FIND:
integral(1/cabin)d(cabin) .... xDD

Exactly: = log cabin+ LinColn

GUSSSSSSSSSSSS

shuning · Apr 29, 2009

回复: Re: 回复: Re: integration

is it cuz i dont get it cuz i do std english? xD

Drongoski · Apr 29, 2009

kwabon said:
sorry, you used u sub right??? i solved this question using u sub, and yeh i dont know what you did in the second line.

thanks

No. I did not. I avoid substituting as far as possible.

shuning · Apr 29, 2009

回复: Re: integration

btw Drongoski.... thank you very much man ^^ u have made me impress my cyber gf ( i think that's the only reason i post questions here 4 LOl )

Trebla · Apr 29, 2009

Re: 回复: Re: integration

shuning said:
that's how ppl in china writes it....

i hardly came across some aus high school students writes it that way... he prob learnd it in uni LOL

NOOB AUS HIGH SCHOOL EDUCATION XD

Heaps of high school students here do it that way. Many teachers (non-asian) teach that method as well.

Timothy.Siu · Apr 29, 2009

Re: 回复: Re: integration

Trebla said:
Heaps of high school students here do it that way. Many teachers (non-asian) teach that method as well.

yeah i do it too, if it saves me a substituion

eldore44 · Apr 29, 2009

Re: 回复: Re: integration

$\sin^{-1}x = u$

$x = \sin u$

$\frac{dx}{dy} = \cos u$

$dx = \cos u . du$

$\int \frac{u \cos u . du}{\sqrt{1 - sin^{2}u}}$

$= \int \frac{u \cos u . du}{\cos u}$

$= \int u.du$

$= \frac{u^{2}}{2}$

at least thats how i got it.
do I then have to put it in terms of x?

Timothy.Siu · Apr 29, 2009

Re: 回复: Re: integration

eldore44 said:
$\sin^{-1}x = u$

$x = \sin u$

$\frac{dx}{dy} = \cos u$

$dx = \cos u . du$

$\int \frac{u \cos u . du}{\sqrt{1 - sin^{2}u}}$

$= \int \frac{u \cos u . du}{\cos u}$

$= \int u.du$

$= \frac{u^{2}}{2}$

at least thats how i got it.
do I then have to put it in terms of x?

thats a really really slow way.

if u want to use that substitution just do

u=sin^-1x
du=1/(root(1-x²) . dx

S u du=u^2/2
and sub it back in.

youngminii · Apr 29, 2009

Re: 回复: Re: integration

Can someone teach me that weird method? I've never seen it before ==;;

GUSSSSSSSSSSSSS · Apr 30, 2009

Re: 回复: Re: integration

lol all it is is writing the 1/sqrt(1 - x^2) as d(inverse(sinx)) **the derivative of sinx**

...?? u get?

shuning · Apr 30, 2009

回复: Re: 回复: Re: integration

Trebla said:
Heaps of high school students here do it that way. Many teachers (non-asian) teach that method as well.

no1 in my school knows it.... ( even the 08ers... and last yr the whole 4u math 28 ppl got 90+ in 4u )

youngminii said:
Can someone teach me that weird method? I've never seen it before ==;;

see this kid never saw it b4 too LOL

GUSSSSSSSSSSSSS · Apr 30, 2009

Re: 回复: Re: 回复: Re: integration

hmmmmmmmmm shuning you MASSIVE contradicting urself

you say heap of chinese know it

then u say no one in ur school know it

YOUR SCHOOL IS CHINESE !!!!!!!!!!!!!
(well at least the math classes are xD)

youngminii · Apr 30, 2009

Re: 回复: Re: 回复: Re: integration

==;; Wthell sif call me a kid.
And no I don't get it.

shuning · Apr 30, 2009

回复: Re: 回复: Re: 回复: Re: integration

GUSSSSSSSSSSSSS said:
hmmmmmmmmm shuning you MASSIVE contradicting urself

you say heap of chinese know it

then u say no one in ur school know it

YOUR SCHOOL IS CHINESE !!!!!!!!!!!!!
(well at least the math classes are xD)

calclus is not in the high school syllbus in china. they only start that in uni. that's y the chinese ppl in my school doesnt know it ^^

and that's y they do conics in yr 9 LOL ( nothing much left there to teach aye when there is no calclus xD )

Dumbledore · Apr 30, 2009

d/dx[arcsin(x)]=1/sqrt(1-x^2) => dx/sqrt(1-x^2) = d(arcsin(x));
thats how we were taught at least

and no i'm not posting during school

Timothy.Siu · Apr 30, 2009

its just changing what ur integrating with respect to.

e.g.

S sinxcosxdx=S sinx d(sinx)=sin²x/2

cutemouse · Apr 30, 2009

Re: 回复: Re: 回复: Re: integration

shuning said:
ibp

lol... You can try that... it wont get you very far.

Dumbledore · Apr 30, 2009

ibp can work
u= arcsin(x) v' = 1/sqrt(1-x^2)
u'=1/sqrt(1-x^2) v = arcsin(x)

S[arcsin(x)/(sqrt(1-x^2)]= arcsin^2(x) - S[arcsin(x)/(sqrt(1-x^2)]
2S[arcsin(x)/(sqrt(1-x^2)]= arcsin^2(x)
S[arcsin(x)/(sqrt(1-x^2)]= 1/2(arcsin^2(x))

but yea... it does suck

shuning · Apr 30, 2009

回复: Re: 回复: Re: 回复: Re: integration

jm01 said:
lol... You can try that... it wont get you very far.

my cyber gf tried it..... she said u had to do it many times and u still get the answer.

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