- #1

- 20

- 0

[tex]\int 4B^{3} x.exp(-2Bx).dx[/tex]

how can i solve this?

it seems easy but i couldn't figure it out

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- Thread starter PullMeOut
- Start date

- #1

- 20

- 0

[tex]\int 4B^{3} x.exp(-2Bx).dx[/tex]

how can i solve this?

it seems easy but i couldn't figure it out

- #2

- 20

- 0

i have to turn my integral into this format and solve the integral.so what to do next?

- #3

tiny-tim

Science Advisor

Homework Helper

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i have to turn my integral into this format and solve the integral.so what to do next?

Hi PullMeOut! Welcome to PF!

You can also write that [tex]\int y^{n} exp(-y) dy =n![/tex] …

so you need to put y = … ?

- #4

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- #5

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I have found it

2Bx=y

dx2B=dy

then put this into the integral. it becomes like

[tex]\int \frac{4B^{3} y^{3}exp(-y) dy}{16B^{4}} [/tex]

then it equals to [tex]\frac{3!}{4B}[/tex] with the help of the integral ı talk about in the previous post

well, i saw your message after i solved it, but thanks anyway tinytim , i really appreciate it :D

2Bx=y

dx2B=dy

then put this into the integral. it becomes like

[tex]\int \frac{4B^{3} y^{3}exp(-y) dy}{16B^{4}} [/tex]

then it equals to [tex]\frac{3!}{4B}[/tex] with the help of the integral ı talk about in the previous post

well, i saw your message after i solved it, but thanks anyway tinytim , i really appreciate it :D

Last edited:

- #6

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i think we can't use 10^k, becaouse it should be the same with dx , so it colud be x^k, but we solved the problem.you can check it out if you want and it is really an easy way.

but thanks for your time

- #7

tiny-tim

Science Advisor

Homework Helper

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i think we can't use 10^k, becaouse it should be the same with dx , so it colud be x^k, but we solved the problem.you can check it out if you want and it is really an easy way.

but thanks for your time

Hi PullMeOut!

Please ignore natives!

Hi natives!

Please don't try to help in homework threads if you don't understand one part of the question, and can't be bothered to read another part of the question.

exp(x) means e

And it is extremely unhelpful to tell an OP to use integration by parts when he has clearly stated "i have to turn my integral into this format and solve the integral"

- #8

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- #9

- 761

- 13

I think Tim agrees with this part.Tiny tim,all I am trying to do is help and/or be helped,if I see other means I'd like to try them out,its a discussion forum not a class!

And I dont think it is polite to tell him to ignore my suggestions,they are merely suggestions he/she can filter them out by themselves without external influence!Thank you.

In this case it is you've brought poor old OP on the wrong foot and you didn't read the question well enough.

- #10

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I think Tim agrees with this part.

In this case it is you've brought poor old OP on the wrong foot and you didn't read the question well enough.

I wish you to have no further discussion over my actions about this,am good at what I do and I know what am doing..My bad I know so much and want to be clear with the alternatives at hand...Am sorry if my attempt was viewed wrong,bringing so thought "complex" mathematics to an OP..I thought its the passion to explore multiple possibilities that drive us all!Am alone.

- #11

HallsofIvy

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Looks to me like integration by parts, taking u= x, dv= exp(-2bx)dx would work nicely.

[tex]\int 4B^{3} x.exp(-2Bx).dx[/tex]

how can i solve this?

it seems easy but i couldn't figure it out

- #12

tiny-tim

Science Advisor

Homework Helper

- 25,832

- 251

Looks to me like integration by parts, taking u= x, dv= exp(-2bx)dx would work nicely.

Hi HallsofIvy!

Yes, but in post #2, he says has has to use a different method.

I assume it's to provide practice at substitution.

(and , in principle, of course, substitution

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