Is it mathematically sound to do this

  • Thread starter brandy
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apply integration by parts twice and swapping the u and v's and then rearranging the equation to say that it is equal to bla/2

like for example i said u is x^n or something and v' is sin x or something.
later on when im faced with another integral, i apply the int by parts but this time the v' is nx^(n-1) and u is -cos x
then i rearangged the equation to say the initial integral is equal to this....

(these u's and v's are NOT the values i had in the equation AND I REALISE THIS DOESNT WORK HERE, i just want to know if the process is sound. because if so, i will be very happy haha)
 

tiny-tim

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hi brandy! :smile:

(try using the X2 icon just above the Reply box :wink:)

yes that's perfectly valid

for example ∫ sinnx dx = [-cosx sinn-1x dx] + (n-1)∫ cos2x sinn-2x dx …

use cos2 = 1 - sin2, and put like terms together :wink:
 

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