• Want to help us with this year's BoS Trials?
    Let us know before 30 June. See this thread for details
  • Looking for HSC notes and resources?
    Check out our Notes & Resources page

how to integrate this? (1 Viewer)

nichhhole

asndihsCfuckingansbdiuahd
Joined
Aug 22, 2006
Messages
605
Location
+GMT 05:00
Gender
Female
HSC
2018
f3nr15 said:
1/ [20t-5t^2]

= [20t-5t^2] ^[-1]

by using ur rule wouldnt we add 1 to n which is [-1]
which would =0....

futhermore..
ax+b is a linear eq...[ie when you differentiate you get a]
wheras the eq we would be using isnt.. [20t-5t^2]...[if we diff here we would get 20-10t.. ]


bah. wdf do we do?
 

Forbidden.

Banned
Joined
Feb 28, 2006
Messages
4,436
Location
Deep trenches of burning HELL
Gender
Male
HSC
2007
chousta said:
wow.....so much effort on such a question........



hot tip: complete the square, and use a result such as invers tan...

well thats wat i would do...
I don't recall inverse trigonometry being in 2-Unit but that sounds like a good idea ...
 

williamc

Active Member
Joined
Sep 6, 2006
Messages
1,398
Location
Sydney
Gender
Male
HSC
2007
jannny said:
huh? wtf is inverse tan .

Can some1 post a completed workout?
If your teacher gave you that question, and you havn't even learnt trignometric functions yet i don't think thats how to do it. I havn't learnt that chapter either yet.
 

Forbidden.

Banned
Joined
Feb 28, 2006
Messages
4,436
Location
Deep trenches of burning HELL
Gender
Male
HSC
2007
nichhhole said:
1/ [20t-5t^2]

= [20t-5t^2] ^[-1]

by using ur rule wouldnt we add 1 to n which is [-1]
which would =0....

futhermore..
ax+b is a linear eq...[ie when you differentiate you get a]
wheras the eq we would be using isnt.. [20t-5t^2]...[if we diff here we would get 20-10t.. ]


bah. wdf do we do?
So far I think the integral should be a natural logarithm or an inverse trigonometric function ...
 

williamc

Active Member
Joined
Sep 6, 2006
Messages
1,398
Location
Sydney
Gender
Male
HSC
2007
nichhhole said:
bah. wdf do we do?
nfi



To the OP where did you get the question from? From what i have learnt so far in 2 unit, i'm pretty sure that isn't a 2 unit question, or the answer is that, that function can not be integrated.
 

Loctorak

New Member
Joined
May 23, 2007
Messages
7
Gender
Male
HSC
2007
f3nr15 said:
I thought you integrated to a natural logarithm (loge f(x))
Isn't that only when the bottom has to do with the differentiation of the first? Or vice versa? In either case I don't think either have very much to do with the differentiation of each other. :)

I'm with the first answer, change it to a negative power and use the function of a function rule. Going from there should be easy.
 

collide

Member
Joined
Mar 23, 2006
Messages
94
Gender
Female
HSC
2007
I did this.. but I'm not sure :S it could be wrong

∫1/20t-5t^2 dt
= 1/20-10t x ∫(20-10t)/20t-5t^2 dt

=1/20-10t x ln (20t-5t^2)

=ln(20t-5t^2)/(20-10t ) + c
 

Forbidden.

Banned
Joined
Feb 28, 2006
Messages
4,436
Location
Deep trenches of burning HELL
Gender
Male
HSC
2007
Loctorak said:
Isn't that only when the bottom has to do with the differentiation of the first? Or vice versa? In either case I don't think either have very much to do with the differentiation of each other. :)

I'm with the first answer, change it to a negative power and use the function of a function rule. Going from there should be easy.
But - 1 + 1 = 0, you can't get a power it must become a natural logarithm instead.

You can use ∫ xn dx = xn+1/n+1 + C, IF n is not equal to 1

collide said:
I did this.. but I'm not sure :S it could be wrong

∫1/20t-5t^2 dt
= 1/20-10t x ∫(20-10t)/20t-5t^2 dt

=1/20-10t x ln (20t-5t^2)

=ln(20t-5t^2)/(20-10t ) + c
I was thinking the VERY same.
Then you could use the quotient rule and check if you are correct.
 

jannny

Member
Joined
Nov 21, 2006
Messages
476
Gender
Male
HSC
2007
collide said:
I did this.. but I'm not sure :S it could be wrong

∫1/20t-5t^2 dt
= 1/20-10t x ∫(20-10t)/20t-5t^2 dt

=1/20-10t x ln (20t-5t^2)

=ln(20t-5t^2)/(20-10t ) + c
I somewat recall my teacher saying you can't take out t or x or y.. because how can u integrate if it is outside the Integral

Oh btw, I got this q from my the school holidays homework.. and I forgot to get the answers sheet.
 

jb_nc

Google "9-11" and "truth"
Joined
Dec 20, 2004
Messages
5,391
Gender
Male
HSC
N/A
this is the answer

Code:
-Log[-4 + x] + Log[x]
---------------------
         20
 

williamc

Active Member
Joined
Sep 6, 2006
Messages
1,398
Location
Sydney
Gender
Male
HSC
2007
The notation in the original question showed the function to be a primitive function. Therefore, it doesn't indicate whether it is a dx or dt function.
 

collide

Member
Joined
Mar 23, 2006
Messages
94
Gender
Female
HSC
2007
jannny said:
I somewat recall my teacher saying you can't take out t or x or y.. because how can u integrate if it is outside the Integral

Oh btw, I got this q from my the school holidays homework.. and I forgot to get the answers sheet.
Yeah I was thinking that as well.. but it just seemed like the most logical way to go about it :S
 

collide

Member
Joined
Mar 23, 2006
Messages
94
Gender
Female
HSC
2007
williamc said:
The notation in the original question showed the function to be a primitive function. Therefore, it doesn't indicate whether it is a dx or dt function.
Oh okay.. I just thought dt indicated that I was integrating with respect to t.
 
P

pLuvia

Guest
You should use partial fractions
Split the denominator into t(20-5t), then use partial fractions then integrate
 
P

pLuvia

Guest
It involves logarithmic methods after the partial fractions has been used
 

jb_nc

Google "9-11" and "truth"
Joined
Dec 20, 2004
Messages
5,391
Gender
Male
HSC
N/A
f3nr15 said:
OLOL wheres your integral calculator ?
No, I did it myself using partial fractions. I wasn't going to type the 10 lines out and I double checked my answer in Matlab and the Integrator.

It's not that hard.
 
Last edited:

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top