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#1 Re: Help Me ! » Integration - Change of Variable » 2007-05-21 22:10:18

fangree01

Hi,

Thanks for all your help. big_smile

#2 Help Me ! » Integration - Change of Variable » 2007-05-21 08:28:04

fangree01
Replies: 3

Hi there,

I hate to be a pain with the change of variable questions but  I have no solutions for the worksheet we were given so I have no idea if I am doing them right so your help is very much appreciated.

The question is ∫x dx/x^4 + 9

My answer is 1/3 tan-¹ x²/3 and I am very unsure of this.

I would be grateful for any help.

Thanks

#3 Re: Help Me ! » Integration » 2007-05-21 07:49:55

fangree01

Hi Mathsyperson,

Thanks for your help, I knew it would be something I was overlooking or looking to hard at dizzy

#4 Re: Help Me ! » Integration » 2007-05-21 07:36:06

fangree01

Hi JaneFairfax,

Thanks for your help and tip I keep forgetting about differentiating to see if I have the right anwser. 

Can I just double check something though  when you integrate someting like e^4x the answer comes out as 1/4 e^4x + C so I was wondering why this did not happen in this question?  This is where I got the -1/32 e^-4x² + c answer, or does this only happen if the question is not a change of variable?

Thanks again for your help up

#5 Help Me ! » Integration » 2007-05-21 03:57:12

fangree01
Replies: 4

Hi,

I was wondering if someone could tell me if I have done this question right?

∫ xe^-4x² dx

OK I made u=4x² to get du=8x and rewrite as xdx=1/8du.  I am not sure if i should have made these negative or not so I went with not.

The answer I got is -1/32 e^-4x² + c.

I am just not sure about the negative thing and if I have intergated the e part right.  dizzy

I would be grateful for any help.

Thanks

#6 Help Me ! » Integrating Trig Functions » 2007-04-01 22:58:10

fangree01
Replies: 1

Hi,

I was wondering if someone could help me with these questions:

a)  ∫2cosx tanx dx
b)  ∫sinx cosx dx
c)  ∫dx/√1-4x²

For a and b I know how to integrate them on their own it's because they are multiplying each other thats getting me.

I would be grateful fpr any help.

Thanks smile

#7 Re: Help Me ! » Integration - Change of Variable (I think) » 2007-03-31 22:52:46

fangree01

Hi JaneFairfax,

Thanks so much for your help its always the simple things that get me. smile

Thank you

#8 Help Me ! » Integration - Change of Variable (I think) » 2007-03-30 22:29:24

fangree01
Replies: 2

Hi I was wondering if someone could help me with these integration questions?

Find   

a  ∫ 2x - 1/ √x dx

b  ∫ (x - 1) (x - 3)/ x² dx

c  ∫ cos³x + 2/ cos²x dx

I have a few ideas but I have no notes on this or solutions so I am not sure if I am doing the right thing.  Any help would be greatly appreciated.

Thanks dizzy

#9 Help Me ! » Complex Numbers Help Plaese!! » 2006-12-12 10:25:16

fangree01
Replies: 1

Hi there,

I was wondering if someone could help with this question.

By putting z = x=iy (x, y ∈ R).  Solve the equation 2z² - z*² + 6z* + 9 = 0.  Were z* is the conjugate of z.

I can do a few of these but i am getting stuck with the 6x i am gettting out of the equation.

I would be grateful for any help.

Thanks

#10 Help Me ! » Nonsingular Matrices » 2006-11-20 10:15:22

fangree01
Replies: 1

Hi,

I was wondering if anyone could help with these questions on matrices i can't get my head around them at all dizzy!!

Let A =     1 -2  -2 -2
               -2  1  -2 -2
               -2 -2   1 -2
               -2 -2  -2  1

Show that (3I - A)² is equal to a certain scalar multiple of 3I - A.  Hence prove that A is nonsingular and find A-¹.

And

Nonsingular nxn matrices A, B are given to satisfy (A + B)-¹ = A-¹ + B-¹.

Show that  C = -C-¹ - I where C = A-¹ B. Deduce that (A-¹ B)³ = I

We have not done the determinant yet so i cant use that i have the answer but i still dont get how to do it.  I would be grateful for any advice.

Thanks

#11 Re: Help Me ! » probabilty » 2006-11-14 04:16:21

fangree01

Hi Mathsyperson,

Thanks for your help are you using p as θ is can they be the same thing?

Also can you help me with the first part:

What is the distribtion of the number of X of contaminated vials in the batch of size n if the overall contamination rate is p?

This was the part i never really got.  Thanks for the tip on variance.

Thanks

#12 Help Me ! » probabilty » 2006-11-13 07:04:04

fangree01
Replies: 3

Hi all,

This is my first time on here and post so hi and thanks in advance for your help!
I am in first year at uni doing probability and ststistics. 
The question i am stuck on is:

What is the distribtion of the number of X of contaminated vials in the batch of size n if the overall contamination rate is p?

What is the expectaion of X?

The info i have is:
n=20
p=0.01

I think i am missing some info,  i have been told to do the binomial distribution, but i missed the lecture on that and i can't work it out!!

I would be greatful for any help and sorry if it makes no sense.

Thanks

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