# intergrationWatch

This discussion is closed.
#1
how do i intergrate things like k/x ? is it something to do with logs? i cant find this in c1 or c2 but i need to do it can neone help?
0
14 years ago
#2
(Original post by sarah12345)
how do i intergrate things like k/x ? is it something to do with logs? i cant find this in c1 or c2 but i need to do it can neone help?
k/x=k multpilied by x^-1

x^-1 when integrated goes to lnx

so you get klnx
0
14 years ago
#3
The integral of 1/x is ln(x). (a standard result)

If you have 1/x multiplied by a constant. i.e. k/x, then just multiply the standard result (1/x) by the same constant.

So if you have k/x then the integral is k.ln(x).
0
14 years ago
#4
Its just k.ln(x)
0
14 years ago
#5
(Original post by sarah12345)
how do i intergrate things like k/x ? is it something to do with logs? i cant find this in c1 or c2 but i need to do it can neone help?
Rewrite it as k(x^-n) and use the formula y' = ax^n, y = [a/(n+1)]x^(n+1). Only use this formula if n =/= -1.

In the case when n=-1, use the fact that y' = kx^(-1), y = klogx.

Euclid.
0
14 years ago
#6
dont forget the constant of integration though.
0
14 years ago
#7
(Original post by evariste)
dont forget the constant of integration though.
Oh them, they're evil. Always catch me out

Euclid.
0
14 years ago
#8
(Original post by Euclid)
Oh them, they're evil. Always catch me out

Euclid.
especially for ln. teachers start calling c things like ln c! confusion all round.
0
#9
thanks for the help!

im trying to do this question

X has a probability density function

f(x)= k/x 1<= x <= 2
0 otherwise

i found that k was 1/ln 2

but now im stuck on finding the expectation and keep getting the wrong answer can anyone help? thanks

also if i know ln x = y how can i work out what x is?
0
14 years ago
#10
E(X) = sum(1 to 2) x*f(x)
=1(1/ln2) + 2(1/2ln2)
=2/ln2

?
0
14 years ago
#11
ln x = y
e^(ln x) = e^y
x = e^y
0
#12
(Original post by kikzen)
ln x = y
e^(ln x) = e^y
x = e^y
thankyou!
0
#13
(Original post by kikzen)
E(X) = sum(1 to 2) x*f(x)
=1(1/ln2) + 2(1/2ln2)
=2/ln2

?
the answer given is 1/ln 2 ?????????????????
0
14 years ago
#14
If the distribution is continuous (not discrete) then you need to integrate x * f(x) between the limits (not sum it).

Then you should get 1/ln 2.

Davros
0
14 years ago
#15
guuhhh i hate stats
0
14 years ago
#16
(Original post by kikzen)
guuhhh i hate stats
dont we all
0
#17
(Original post by davros)
If the distribution is continuous (not discrete) then you need to integrate x * f(x) between the limits (not sum it).

Then you should get 1/ln 2.

Davros
so is this right?

i intergrate between 1 and 2 x* k/x which would just give me k?
0
14 years ago
#18
Yes, and you have already worked out what k is...
0
#19
(Original post by davros)
Yes, and you have already worked out what k is...
thankyou for all the help!
0
X
new posts
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### University open days

• University of East Anglia
All Departments Open 13:00-17:00. Find out more about our diverse range of subject areas and career progression in the Arts & Humanities, Social Sciences, Medicine & Health Sciences, and the Sciences. Postgraduate
Wed, 30 Jan '19
• Aston University
Wed, 30 Jan '19
• Solent University
Sat, 2 Feb '19

### Poll

Join the discussion

Remain (1365)
79.73%
Leave (347)
20.27%