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Mathematics 16 Online
OpenStudy (christos):

Can you please help me solve this ? https://www.dropbox.com/s/u2j3kptjtn6vvxz/Screenshot%202013-11-04%2008.00.03.jpg

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

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

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

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

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

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) ?

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 :)

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

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 :)

OpenStudy (christos):

btw why are those labelled as "improper integrals" ??

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