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Mathematics 8 Online
OpenStudy (anonymous):

Just a small question...

OpenStudy (anonymous):

Having something like this... \[\lim _{x \rightarrow0}e ^{(\frac{ 3 }{ x })\ln(1-3x)}\] is it possible to bring the e out and get this... \[e \lim _{x \rightarrow0}(\frac{ 3 }{ x })\ln (1-3x)\]

OpenStudy (solomonzelman):

\(\large\color{black}{ \displaystyle \lim_{x\rightarrow 0}e^{\frac{3}{x}\ln(1-3x)} }\) \(\large\color{black}{ \displaystyle e^{\lim_{x\rightarrow 0}\frac{3}{x}\ln(1-3x)} }\)

OpenStudy (solomonzelman):

is this better ?

OpenStudy (anonymous):

Oh yes! That's it! But what's the logic behind this step? I don't exactly understand

OpenStudy (solomonzelman):

you should review the limit properties

OpenStudy (anonymous):

Hmmm ok gotcha!

OpenStudy (solomonzelman):

I mean, nothing offensive, but find a link and read them over. you can find them absolutely everywhere

OpenStudy (anonymous):

No worries at all! Thanks for the help!

OpenStudy (solomonzelman):

\(\LARGE\color{black}{ \displaystyle e^{\lim_{x\rightarrow 0}\frac{3\ln(1-3x)}{x}} }\) \(\LARGE\color{black}{ \displaystyle e^{-\lim_{x\rightarrow 0}\frac{3\ln(1-3x)}{-x}} }\)

OpenStudy (solomonzelman):

did this step just now make sense?

OpenStudy (solomonzelman):

now both top and bottom go to -infinity

OpenStudy (solomonzelman):

go ahead and apply L'H's

OpenStudy (anonymous):

Is that the same as what you wrote before? (e^ lim....)

OpenStudy (solomonzelman):

I didn't change the value. I didn't do any unallowed step

OpenStudy (solomonzelman):

am I allowed to multiply times -1 twice? (on the bottom and in front of the lim)

OpenStudy (solomonzelman):

\(\LARGE\color{black}{ \displaystyle e^{\lim_{x\rightarrow 0}\frac{3\ln(1-3x)}{x}} }\) \(\LARGE\color{black}{ \displaystyle e^{-\lim_{x\rightarrow 0}\frac{3\ln(1-3x)}{-x}} }\)

OpenStudy (solomonzelman):

now apply the lhs to the limit. questions about how I got till there?

OpenStudy (anonymous):

would we have to multiply by -1 ?

OpenStudy (solomonzelman):

what do you mean? where?

OpenStudy (solomonzelman):

I already got it to approach -oo

OpenStudy (solomonzelman):

to approach -oo on top and bottom

OpenStudy (anonymous):

Ohhh but it should be approaching 0

OpenStudy (solomonzelman):

oh, I mean 0

OpenStudy (solomonzelman):

it is.

OpenStudy (solomonzelman):

ln(1-0)=1 -x=-0=0

OpenStudy (solomonzelman):

why am I saying -oo ? apologize

OpenStudy (solomonzelman):

\(\LARGE\color{black}{ \displaystyle e^{-\lim_{x\rightarrow 0}\frac{3\ln(1-3x)}{-x}} }\) top and bottom DO go to 0. ln(1)=0 and -(0)=0

OpenStudy (anonymous):

So it's just the first line right?

OpenStudy (anonymous):

I mean I don't get why we'd have a -lim and -x in the denominator

OpenStudy (solomonzelman):

\(\LARGE\color{black}{ \displaystyle e^{\lim_{x\rightarrow 0}\frac{3\ln(1-3x)}{x}} }\)

OpenStudy (solomonzelman):

it was my mistake, i was thinking of infinity b/c i thought the lim -> (-oo)

OpenStudy (solomonzelman):

but in can x->0 take LHS as it is

OpenStudy (solomonzelman):

\(\LARGE\color{black}{ \displaystyle e^{\lim_{x\rightarrow 0}\frac{3\ln(1-3x)}{x}} }\) \(\huge \color{black}{ \displaystyle e^{\lim_{x\rightarrow 0}\frac{3\frac{-3}{1-3x}}{1}} }\)

OpenStudy (anonymous):

Oh okie dokie! So now its just L'Hopital right?

OpenStudy (solomonzelman):

yes... that i did d/dx on top and bottm

OpenStudy (solomonzelman):

\(\huge \color{black}{ \displaystyle e^{\lim_{x\rightarrow 0}\frac{-9}{1-3x}} }\)

OpenStudy (anonymous):

I get -9 on the top but on the bottom isn't the derivative of x just 1?

OpenStudy (solomonzelman):

yes, 3 replies ago i did the derivative

OpenStudy (anonymous):

Ohh cause its a fraction over a fraction!

OpenStudy (anonymous):

Yeah got it!!

OpenStudy (solomonzelman):

wel, 1 on bottom for x, and the derivative of ln(1-3x) is a fraction -3/(1-3x)

OpenStudy (solomonzelman):

ok, what is your answer?

OpenStudy (anonymous):

is it e^-9 ? So 1/e^9

OpenStudy (solomonzelman):

yes, there you go!

OpenStudy (solomonzelman):

I can review the limit properties with you if you want...

OpenStudy (anonymous):

Finally! Haha! Thanks so much! I've been bugging you a lot today! Im so sorry!

OpenStudy (solomonzelman):

Ok, you welcome. You can choose to rvw limit properties later alone, or if you would like to, I can type more here...

OpenStudy (anonymous):

That's fine! I can look it up on Google real quick! :D

OpenStudy (anonymous):

Thanks again!

OpenStudy (solomonzelman):

Alright. Enjoy:) ... not a problem.

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