Mathematics
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OpenStudy (christos):
Can you please help me solve this ?
https://www.dropbox.com/s/u2j3kptjtn6vvxz/Screenshot%202013-11-04%2008.00.03.jpg
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hartnn (hartnn):
did you try 1-e^-x as u ?
OpenStudy (anonymous):
1-e^-x = t^2......sunstitution
OpenStudy (anonymous):
subs**
hartnn (hartnn):
why t^2 ? and not t ?
OpenStudy (anonymous):
coz of root.....it will blow out sqrt
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OpenStudy (christos):
I get int from 0 to 0 of du/u
hartnn (hartnn):
when x = infinity , e^-inf = 0
OpenStudy (christos):
yes thats why I say 0 to 0
hartnn (hartnn):
but t^2 will make dt complicated
hartnn (hartnn):
1-e^-x = 1
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hartnn (hartnn):
1-e^-x as u
OpenStudy (anonymous):
result will be same....i prefer t^2 @hartnn
hartnn (hartnn):
ohh, if result same than ok :)
OpenStudy (christos):
hartnn ?
hartnn (hartnn):
the function is 1-e^-x = u
so the new limits are 0 to 1
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OpenStudy (christos):
wait if u = 1 - e^-x
OpenStudy (christos):
u 1 - e^-0
OpenStudy (christos):
u = 1 - 1
OpenStudy (christos):
u = 0
hartnn (hartnn):
for x= 0, u=0
for x =infinity, u=1
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OpenStudy (christos):
u = 1 -e-inf
OpenStudy (christos):
u = 1 - 0 aah
hartnn (hartnn):
and integrate du/sqrt u from 0 to 1
OpenStudy (christos):
ln|1| - ln|0|
OpenStudy (anonymous):
if you are having prob in values of e^x then remember its graph as sign of nike
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hartnn (hartnn):
sqrt u = u^(1/2)
you won't get du/u
you get du/sqrt u
OpenStudy (christos):
ln|sqrt(1)| - ln|sqrt(0)|
hartnn (hartnn):
how are you even getting ln ?
hartnn (hartnn):
for 1/sqrt u
use
integral x^n formula
u^(-1/2) du
OpenStudy (christos):
so its 2sqrt(1) - 2sqrt(0) ?
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OpenStudy (christos):
oh wait I'm confused now , lol
hartnn (hartnn):
n= -1/2
n+1 = ... ?
OpenStudy (christos):
my answer with 3 in the denominators
OpenStudy (anonymous):
see mine one was good @hartnn
hartnn (hartnn):
you can show your method too :)
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hartnn (hartnn):
n= -1/2
n+1 = ... ?
@Christos
OpenStudy (christos):
n= -1/2
n+1 = 1/2
hartnn (hartnn):
so, integral u^(-1/2) du = (1/2) sqrt u
got this ?
hartnn (hartnn):
oops, its divided by (1/2)
so yeah
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OpenStudy (christos):
with a 2 as a coeff right ?
OpenStudy (christos):
yea, so my answer was correct ??
hartnn (hartnn):
so its 2sqrt(1) - 2sqrt(0) ? <<<<< correct
OpenStudy (christos):
Nice :D
hartnn (hartnn):
divu, you can show your method now if you want to :)
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OpenStudy (christos):
btw why are those labelled as "improper integrals" ??