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amyna
 one year ago
find intergal:
this is an interrogation by parts problem
amyna
 one year ago
find intergal: this is an interrogation by parts problem

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amyna
 one year ago
Best ResponseYou've already chosen the best response.0i got: u=x^3 du=3x^2 dv=e^x^2 v= i don't know lol

freckles
 one year ago
Best ResponseYou've already chosen the best response.5\[u=x^2 \\ du=2x dx \\ \text{ now multiply both sides of } du=2x dx \text{ by } \frac{1}{2}x^2 \\ \text{ so we have } \\ \frac{1}{2}x^2 du=x^3 dx \\ \text{ but recall } x^2=u \\ \text{ so we have } \frac{1}{2}u du=x^3 dx\] once I make this substitution then I would do integration by parts

freckles
 one year ago
Best ResponseYou've already chosen the best response.5or you could have actually went with the sub u=x^2 instead

amyna
 one year ago
Best ResponseYou've already chosen the best response.0ok i'll try and do this, and see what i get. thanks!

amyna
 one year ago
Best ResponseYou've already chosen the best response.0ya i don't know what I'm doing! can i use integration by parts first?

Jhannybean
 one year ago
Best ResponseYou've already chosen the best response.0this is an interrogation huh? ;)

freckles
 one year ago
Best ResponseYou've already chosen the best response.5you could try integration by parts but as you wrote earlier it is a little confusing to do a substitution would make the integration by parts less confusing  what do you mean you don't know what you are doing? like you couldn't do the substitution I gave you above ?

amyna
 one year ago
Best ResponseYou've already chosen the best response.0ya where did you get the x^3 from?

freckles
 one year ago
Best ResponseYou've already chosen the best response.5\[\int\limits x^3 e^{x^2} dx \\ \text{ replace } x^2 \text{ with } u \\ \text{ replace } x^3 dx \text{ with } \frac{1}{2} u du \\ \text{ giving you } \\ \int\limits \frac{1}{2} u e^{u} du\]

freckles
 one year ago
Best ResponseYou've already chosen the best response.5did you read the third line ?

freckles
 one year ago
Best ResponseYou've already chosen the best response.5\[u=x^2 \\ du=2x dx \\ \text{ now multiply both sides of } du=2x dx \text{ by } \frac{1}{2}x^2 \\ \text{ so we have } \\ \frac{1}{2}x^2 du=x^3 dx \\ \text{ but recall } x^2=u \\ \text{ so we have } \frac{1}{2}u du=x^3 dx\] that third line said I multiplied both sides by 1/2x^2

amyna
 one year ago
Best ResponseYou've already chosen the best response.0oh okay! thats more clear! Thanks!

freckles
 one year ago
Best ResponseYou've already chosen the best response.5it was just a copy and paste of what I said earlier :p \[\frac{1}{2}x^2 \cdot 2x dx =\frac{2}{2} x^3 dx=x^3 dx\]

Jhannybean
 one year ago
Best ResponseYou've already chosen the best response.0where is this \(\dfrac{1}2x^2\) coming from...

freckles
 one year ago
Best ResponseYou've already chosen the best response.5we have to write x^3 dx in terms of u

freckles
 one year ago
Best ResponseYou've already chosen the best response.5that is where it comes from

Jhannybean
 one year ago
Best ResponseYou've already chosen the best response.0Oh nevermind, it's to eliminate the 2 and to obtain x\(^3\) on the right side. Nvm.

jacobciezki
 one year ago
Best ResponseYou've already chosen the best response.0Why are you girls still in her
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