HSC 2012 MX1 Marathon #2 (archive) (1 Viewer)

[barbernator]

Re: HSC 2012 Marathon

why doesn't the general formula work to integrate

integral e^ln(x) = e^f(x)/f'(x) = e^ln(x)/1/x = x^2 =/= x^2/2

i know that it can just be simplified to x, but im wondering why the formula doesn't work

 

[Kingportable]

Re: HSC 2012 Marathon

Any ideas though?

 

[Timske]

Re: HSC 2012 Marathon

isnt it f'(x)/f(x) ?

 

[barbernator]

Re: HSC 2012 Marathon

lol

did i just make an extremely rookie error?

 

[Timske]

Re: HSC 2012 Marathon

integral e^lnx = f'(x)/f(x) = 1/x

woops

 

[bleakarcher]

Re: HSC 2012 Marathon

integral e^lnx = f'(x)/f(x) = 1/x

woops

shitballs

I just got on the forums again and I see this..

 

[barbernator]

Re: HSC 2012 Marathon

integral e^lnx = f'(x)/f(x) = 1/x

woops

ok now u guys can lol at me, does that give me permission to lol at this?

 

[barbernator]

Re: HSC 2012 Marathon

why doesn't the general formula work to integrate

integral e^ln(x) = e^f(x)/f'(x) = e^ln(x)/1/x = x^2 =/= x^2/2

i know that it can just be simplified to x, but im wondering why the formula doesn't work

but 4srs, i know that e^ln(x)=x. but why can u not use e^f(x)/f'(x) to integrate instead. Is it something to do with the domain of the function?

 

[Carrotsticks]

Re: HSC 2012 Marathon

Oooh, if you could find it, can you post it again. A nice question that I remember you posting was how to integrate 1/1+tan^n(x) between 0 and pi/2 but that needs 4U techniques...

I don't remember that question... Anyway here it is:

 

[barbernator]

Re: HSC 2012 Marathon

LOL comments removed deswa and nightweaver hehe

 

[Timske]

Re: HSC 2012 Marathon

but 4srs, i know that e^ln(x)=x. but why can u not use e^f(x)/f'(x) to integrate instead.

because e^lnx = x thats why hahah

 

[Kingportable]

Re: HSC 2012 Marathon

John Fitzpatrick 3U Mathematics 25(c) Question 3

A particle movies in a straight line. At time t seconds, its displacement x cm from a fixed poin O in the line is given by x=5sin((pi/2)T + pi/6). Express the acceleration in terms of x only and hence show that the motion is simple harmonic. Find:

iii) The speed when x=-2+1/2
iv) the acceleration when x = -2 + 1/2

 

[Timske]

Re: HSC 2012 Marathon

John Fitzpatrick 3U Mathematics 25(c) Question 3

A particle movies in a straight line. At time t seconds, its displacement x cm from a fixed poin O in the line is given by x=5sin((pi/2)T + pi/6). Express the acceleration in terms of x only and hence show that the motion is simple harmonic. Find:

iii) The speed when x=-2+1/2
iv) the acceleration when x = -2 + 1/2

x=-2+1/2 do you mean -2.5?

 

[deswa1]

Re: HSC 2012 Marathon

LOL comments removed deswa and nightweaver hehe

Ahh you noticed. I removed it because I didn't read your question properly and I didn't want to look like a retard if I was wrong. What is your question?

 

[barbernator]

Re: HSC 2012 Marathon

Ahh you noticed. I removed it because I didn't read your question properly and I didn't want to look like a retard if I was wrong. What is your question?

the question is, why when integrating e^ln(x) through both methods e^f(x)/f'(x) and x yield different results?

 

[deswa1]

Re: HSC 2012 Marathon

the question is, why when integrating e^ln(x) through both methods e^f(x)/f'(x) and x yield different results?

How can you integrate e^ln(x) using this. If f(x)=ln(x), then f'(x)=1/x. Therefore to use this form, you would have to be integrating (1/x)(e^ln(x)) not just e^ln(x)

 

[Carrotsticks]

Re: HSC 2012 Marathon

the question is, why when integrating e^ln(x) through both methods e^f(x)/f'(x) and x yield different results?

How did you get the bolded part? That is only applicable if f'(x) is a constant...

 

[Kingportable]

Re: HSC 2012 Marathon

x=-2+1/2 do you mean -2.5?

yes, btw i tried using x''=-n^2 . x and v^2=n^2 . (a^2 + x^2)

My problem with differentiation from the displacement was that i didn't have a value for t

 

[nightweaver066]

Re: HSC 2012 Marathon

Ahh you noticed. I removed it because I didn't read your question properly and I didn't want to look like a retard if I was wrong. What is your question?

Same, then i realised his question is troll.

 

[nightweaver066]

Re: HSC 2012 Marathon

I don't remember that question...

The question that you got from one of your students; that i indirectly sent you