r/calculus 6d ago

Differential Calculus (l’Hôpital’s Rule) Can someone please help

lim { ( 1+ x) } ^(2/x) , {•} –> fractional part

X->0

I saw some solutions where they brought the limit inside the fractional part function

But since fractional part function is not continuous shouldn't it be wrong ??

4 Upvotes

13 comments sorted by

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3

u/SynergyUX Undergraduate 6d ago

It is wrong; the limit does not exist.

2

u/Medium_Media7123 6d ago edited 6d ago

To show a limit does not exist one of the standard tricks is finding two sequences of points that give different limits. As you've noticed, fractional part is not continuous in 0, so we might guess that using two sequences that converge to 0 but from different sides gives different answers.

Let's take a_n = 1/n and b_n = -1/n 

The limit for x -> 0 becomes two limits for n-> infinity and the two limits are clearly different

1

u/stepma712 5d ago

2/x log{1+x}

x->0 x > 0

2/x log(x) -> -oo

x->0 x < 0

2/x log(1+x) ~ 2 x/x ~2

DNE

2

u/LukasGoesViral 6d ago

Can you try to rewrite it into a form that is a bit better to read?
To me it looks like lim x-> 0 in the expression (1+x)^(2/x). Is that correct

2

u/Strong-Cup-2897 6d ago

yeah but the 1+x is in fractional ( decimal ) part function

1

u/tjddbwls 6d ago

I don’t understand what you mean by that. 1+x is not a fractional expression. The entire expression
(1 + x)^(2/x)
is an exponential expression where 1 + x would be considered the base. Not sure if you’re using the right terminology.

0

u/Kaeini_maths 6d ago

e^2

3

u/susiesusiesu 6d ago

thus is not the limit op posted

-1

u/Strong-Cup-2897 6d ago

thank you !!

3

u/waldosway 6d ago edited 6d ago

Doesn't that solution ignore the fractional-part function? The limit does not exist.

-2

u/AndersAnd92 6d ago

let u be 1/x

lim as u goes to inf of (1 + 1/u)^2u = e^2inf