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# Can someone go through this question with me step by step? U Substitution watch

1. I am trying and failing to wrap my head around this question ugh
2. (Original post by Dinasaurus)

I am trying and failing to wrap my head around this question ugh
Find dx/du. Change the limits of integration. Write out the integral with the new limits and with dx/du du in place of dx, not putting things in terms of u right away, and see if anything cancels nicely. Then if you've done it right you need a simple "creative adding of zero" so to speak.
lol no you don't you just do the fractions normally, I am very tired
3. (Original post by Dinasaurus)

I am trying and failing to wrap my head around this question ugh
If then

You can do that because you can pretend that the du's cancel so: .

So, plugging in the relevant bits:

Then notice that

and that .
4. (Original post by 13 1 20 8 42)
Find dx/du. Change the limits of integration. Write out the integral with the new limits and with dx/du du in place of dx, not putting things in terms of u right away, and see if anything cancels nicely. Then if you've done it right you need a simple "creative adding of zero" so to speak.
lol no you don't you just do the fractions normally, I am very tired
I found dx as 1/-3x^2 du

The main issue I have is the fraction, I don't know how to substitute the x^5 on the numerator.

-u+3 = x^3

Should I multiply both parts by the power of 5/3?
5. (Original post by Zacken)
.
Use the subsitution ....
6. (Original post by 16Characters....)
Use the subsitution ....
I must be going blind! Thanks, I think I've edited it and it should be fixed. Embarrassing much...
7. (Original post by Dinasaurus)
I found dx as 1/-3x^2 du

The main issue I have is the fraction, I don't know how to substitute the x^5 on the numerator.

-u+3 = x^3

Should I multiply both parts by the power of 5/3?
No, it cancels in the integral with the dx/du to give you something you can express more easily
8. (Original post by 13 1 20 8 42)
No, it cancels in the integral with the dx/du to give you something you can express more easily
I got down to u-3/3u

Damn that looks a lot more doable.
9. (Original post by Dinasaurus)
I got down to u-3/3u

Damn that looks a lot more doable.
think that's right
10. (Original post by 13 1 20 8 42)
think that's right

am I too late?
11. (Original post by TeeEm)
am I too late?
It would appear so
12. (Original post by 13 1 20 8 42)
It would appear so
my new catchphrase ...
13. Ooh looks fun, but IM LATE IM LATE FOR A VERY IMPORTANT DATE!
😏

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