indefinate integral

SoundTheSurrender

Diamond Member
Mar 13, 2005
3,126
0
0
So here is the problem...

/ (z)/ root (z+5) dz

it can be turned to

/ (z)(z+5)^(-1/2)



u = (z+5)

du = 1

dx = 1

Then I'm lost from here because I'm not sure what to do.

Thanks.
 

Elderly Newt

Senior member
May 23, 2005
430
0
0
Originally posted by: djmihow
So here is the problem...

/ (z)/ root (z+5) dz

it can be turned to

/ (z)(z+5)^(-1/2)



u = (z+5)

du = 1

dx = 1

Then I'm lost from here because I'm not sure what to do.

Thanks.

ok... your dx=1 should be dz=1
then, you take your expression
/ (z)(z+5)^(-1/2) dz
and substitute your u and dz in and you get
/ (z)u^(-1/2)
now you have a z in there!
so go back to your u equation
u = z+5
and solve for z
z = u-5
substitute that for z and you get
/ (u-5)u^(-1/2)
and then... i think you distribute that.. and you get
/ u^(1/2) - 5u^(-1/2)
and now you can do basic intergration on that

hmm ok... i hope thats right.. somebody pleeeaase correct me if i did something wrong!
 

aux

Senior member
Mar 16, 2002
533
0
0
Originally posted by: Elderly Newt
Originally posted by: djmihow
So here is the problem...

/ (z)/ root (z+5) dz

it can be turned to

/ (z)(z+5)^(-1/2)



u = (z+5)

du = 1

dx = 1

Then I'm lost from here because I'm not sure what to do.

Thanks.

ok... your dx=1 should be dz=1
then, you take your expression
/ (z)(z+5)^(-1/2) dz
and substitute your u and dz in and you get
/ (z)(u^-1/2)
now you have an a z in there!
so go back to your u equation
u = z+5
and solve for z
z = u-5
substitute that for z and you get
/ (u-5)(u^-1/2)
and then... i think you distribute that.. and you get
/ (u^1/2)-5u^-1/2
and now you can do basic intergration on that

hmm ok... i hope thats right.. somebody pleeeaase correct me if i did something wrong!

Looks about right, but the notation can be confusing for the OP.
u^-1/2 is better written as u^(-1/2) or, (the same) 1/sqrt(u), or (using OP's notation) 1/root(u)



 

SoundTheSurrender

Diamond Member
Mar 13, 2005
3,126
0
0
I have this problem.

(1+x^2)/(x^2) Dx

so.. do I change it to

(1+x^2)(x^-2) ?

I don't know what to do with d and du... they don't form right.

 

hypn0tik

Diamond Member
Jul 5, 2005
5,867
2
0
Originally posted by: djmihow
I have this problem.

(1+x^2)/(x^2) Dx

so.. do I change it to

(1+x^2)(x^-2) ?

I don't know what to do with d and du... they don't form right.

Split up the numerator.

(1+x^2)/x^2 = 1/x^2 + x^2/x^2 = 1/x^2 + 1

The rest should be straight forward.

Edit: I guess if it makes it easier to integrate, you can write it as x^-2 + 1. Either way, the result is the same.
 

SoundTheSurrender

Diamond Member
Mar 13, 2005
3,126
0
0
so it should be.

1x^(-2)+1dx

1 / x^-2 dx + 1 / dx / = represents the integrate sign

then

x^(-1)/1 +1x

1/x + 1x

but it should be 1/x - 1x.... I don't know how to get a negative?

according to my calculator, it should = 4.8 because it goes from 1 to 5...


 

hypn0tik

Diamond Member
Jul 5, 2005
5,867
2
0
The integral of 1/x^2 + 1 dx = -1/x + x

You may be missing a negative sign in your original integral.
 

MichaelD

Lifer
Jan 16, 2001
31,529
3
76
Originally posted by: aux
Originally posted by: Elderly Newt
Originally posted by: djmihow
So here is the problem...

/ (z)/ root (z+5) dz

it can be turned to

/ (z)(z+5)^(-1/2)



u = (z+5)

du = 1

dx = 1

Then I'm lost from here because I'm not sure what to do.

Thanks.

ok... your dx=1 should be dz=1
then, you take your expression
/ (z)(z+5)^(-1/2) dz
and substitute your u and dz in and you get
/ (z)(u^-1/2)
now you have an a z in there!
so go back to your u equation
u = z+5
and solve for z
z = u-5
substitute that for z and you get
/ (u-5)(u^-1/2)
and then... i think you distribute that.. and you get
/ (u^1/2)-5u^-1/2
and now you can do basic intergration on that

hmm ok... i hope thats right.. somebody pleeeaase correct me if i did something wrong!

Looks about right, but the notation can be confusing for the OP.
u^-1/2 is better written as u^(-1/2) or, (the same) 1/sqrt(u), or (using OP's notation) 1/root(u)


The two of you just killed what few remaining brain cells I had left. I know that people like you design the bridges I drive over every day...thank you for being so smart!

For the life of me; I'll never understand these....THINGS that you figure out with such ease.

You read the problem. You thought about it. You solved it.

To me, I see this:

Take the equation Y%w3/>^550.ee.
Add 1.56 kilograms of apples
Subtract one French Apple Pie of unknown weight
A dog of unknown size pees on it
A full moon shines ONLY 44% of it's available ultraviolet light on it
The square is 0)98(8*&6?@>>NULL
Enter your result here =



 

6shiw1

Member
Mar 8, 2005
165
0
0
lol, calculus? I thought most of AT would have been familiar with integration as a sophomore in highschool.
 

archcommus

Diamond Member
Sep 14, 2003
8,115
0
71
I just finished calc 3 last semester so after that my brain automatically purged all calc knowledge.

Sorry, can't help.
 

xSauronx

Lifer
Jul 14, 2000
19,586
4
81
Originally posted by: 6shiw1
lol, calculus? I thought most of AT would have been familiar with integration as a sophomore in highschool.

heh, i didnt even get to finish my geometry classes. my math ability is pathetic.
 
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