## anonymous one year ago Getting slightly wrong answer trying to integrate y*sqrt(y-2) by parts

1. anonymous

2. anonymous

$\int y\sqrt{y-2}dy$?

3. anonymous

Yes. WolframAlpha gives me: http://www.wolframalpha.com/input/?i=integrate+y*sqrt%7By-2%7D which is not my answer. Can't figure out what I'm doing wrong.

4. anonymous

first off i would not integrate by parts unless you are told you have to

5. anonymous

Good point.

6. zepdrix

There's a nice simple u-substitution for this one :) Not seeing it?

7. zepdrix

It a neat little trick that maybe you haven't considered.$\large\rm \color{orange}{u=y-2}\qquad\to\qquad \color{red}{u+2=y}$$\large\rm \color{blue}{du=dy}$ $\large\rm \int\limits \color{red}{y}\sqrt{\color{orange}{y-2}}~\color{blue}{dy}=?$Do you see how that will help here? :o

8. anonymous

Thanks so much for the help, but I already solved it with u-substitution and am just utterly stumped as to why I can't get the right answer with integration by parts. Should I just give up on that? :)

9. zepdrix

Oh :o checking

10. zepdrix

ok i think i see a boo boo...

11. zepdrix

|dw:1442370147408:dw|Missing a 2 here :o

12. zepdrix

Did that maybe throw things off a bit?

13. anonymous

AH! That was it. Thank you very much!