The Student Room Group
Reply 1
Substitute u = x^2.
Reply 2
DFranklin
Substitute u = x^2.


could i make the substitution x=2x^2? Would that not be easier?
Reply 3
irish_4_life
could i make the substitution x=2x^2? Would that not be easier?

u =-2x^2 would be easier than that
Reply 4
rbnphlp
-2x^2 would be easier than that


okay so let's let S = intergration sign... then i get?

S xe^u dx and xdx=1/4du

So

1/4 S e^u du? still in between k and 0? Yes? no? hah
Reply 5
irish_4_life
could i make the substitution x=2x^2? Would that not be easier?

I didnt notice it was x , you mean u surely...
Reply 6
irish_4_life
okay so let's let S = intergration sign... then i get?

S xe^u dx and xdx=1/4du

So

1/4 S e^u du? still in between k and 0? Yes? no? hah

yes thats right..
rbnphlp
yes thats right..


Really??
Reply 8
ghostwalker
Really??

S= integral

-1/4 S e^u du between k and 0 ( however,Iam assuming he is going to make the substitution u=-2x^2 after the integration so that the limits will work)

he missed the - sign looking at it again other than I dont know what else is wrong
Reply 9
rbnphlp
I didnt notice it was x , you mean u surely...


Yeah you're right! :smile: - i've got it now thanks guys! x
Reply 10
irish_4_life
Yeah you're right! :smile: - i've got it now thanks guys! x

did you change the limits or (change e^u into e^-2x^2and then use the limits between k and 0)and you left -sign , I m sure thats what ghostwalker was asking if it was right...
rbnphlp
S= integral

-1/4 S e^u du between k and 0 ( however,Iam assuming he is going to make the substitution u=-2x^2 after the integration so that the limits will work)

he missed the - sign looking at it again other than I dont know what else is wrong


Yep.