how to integrate this? (1 Viewer)

[nichhhole]

?

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.]

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]

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.]

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]

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]

I thought you integrated to a natural logarithm (log_e 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]

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.]

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

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]

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]

this is the answer

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

 

[williamc]

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.

 

[williamc]

this is the answer

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

Show working please. NFI how you got that answer.

 

[collide]

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]

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.

 

[pLuvia]

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

 

[Forbidden.]

this is the answer

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

OLOL wheres your integral calculator ?

Show working please. NFI how you got that answer.

It's a bit long, he / his integral calculator is correct. (I think the latter)

I KNEW it involved natural logarithms ...

 

[pLuvia]

It involves logarithmic methods after the partial fractions has been used

 

[jb_nc]

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.