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 [Maths] Proving~~

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withoutwax
Professor
Professor
withoutwax


Posts : 101
Join date : 2008-08-02

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PostSubject: [Maths] Proving~~   [Maths] Proving~~ Icon_minitimeSat Sep 13, 2008 4:34 pm

Exam's over..but we never let our brain stops..

Just found a few interesting question..try it out~~

Prove

{integral} 1/sinx dx=ln{tan[1/2 x]} + C

and

{integral} 1/cosx dx=ln{[cos x]/[1-sin x]} + C

Happy working it~~Whahaha bounce bounce bounce bounce bounce
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withoutwax
Professor
Professor
withoutwax


Posts : 101
Join date : 2008-08-02

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PostSubject: Re: [Maths] Proving~~   [Maths] Proving~~ Icon_minitimeTue Sep 16, 2008 8:08 pm

No one is willing to giv a damn-try on this??
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mia

mia


Posts : 63
Join date : 2008-08-01

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PostSubject: Re: [Maths] Proving~~   [Maths] Proving~~ Icon_minitimeWed Sep 17, 2008 12:24 am

Hmm...

{integral} 1/sinx dx
I got is ln tanx...
cos differentiate sinx is cos x and integrate 1/sinx would be ln sinx...
haha.... so eventually is (ln sinx)/(cos x) and thus ln tanx
XD.... I know it must be wrong.... but thats how I see it...

for {integral} 1/cosx dx
I thought will get (-ln cos x)/(sin x) ?
LOL...
cos differentiate cosx is -sin x.... how dya get 1-sinx?? confused
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Death
V.I.P.
V.I.P.
Death


Posts : 368
Join date : 2008-08-05
Location : Milky Way Galaxy

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PostSubject: Re: [Maths] Proving~~   [Maths] Proving~~ Icon_minitimeWed Sep 17, 2008 12:31 pm

mia wrote:
Hmm...

{integral} 1/sinx dx
I got is ln tanx...
cos differentiate sinx is cos x and integrate 1/sinx would be ln sinx...
haha.... so eventually is (ln sinx)/(cos x) and thus ln tanx
XD.... I know it must be wrong.... but thats how I see it...

for {integral} 1/cosx dx
I thought will get (-ln cos x)/(sin x) ?
LOL...
cos differentiate cosx is -sin x.... how dya get 1-sinx?? confused

I think we has to use trigonometric identity,sin^2 x + cos^2 x = 1,or the sin x = 2t / 1+t^2 or something..
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withoutwax
Professor
Professor
withoutwax


Posts : 101
Join date : 2008-08-02

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PostSubject: Re: [Maths] Proving~~   [Maths] Proving~~ Icon_minitimeWed Sep 17, 2008 6:38 pm

Yup..you're rite Death..

Advice to Mia: y don't you diffrentiate ur ans bak..see if u get the ans anot?
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angie




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Join date : 2008-09-16

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PostSubject: Re: [Maths] Proving~~   [Maths] Proving~~ Icon_minitimeWed Sep 24, 2008 10:45 pm

wakaka~~ let t= tan 1/2 x first~~ hehe~~ then start integrate the 1/sin x.... hehe Surprised flower
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withoutwax
Professor
Professor
withoutwax


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PostSubject: Re: [Maths] Proving~~   [Maths] Proving~~ Icon_minitimeThu Sep 25, 2008 11:06 am

wow..so geng?? try integrate the other one too..
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flamenix

flamenix


Posts : 27
Join date : 2008-08-05

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PostSubject: Re: [Maths] Proving~~   [Maths] Proving~~ Icon_minitimeSun Sep 28, 2008 12:14 am

I had done it.. A good question..
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PostSubject: Re: [Maths] Proving~~   [Maths] Proving~~ Icon_minitime

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