Can't find $lim_xto-1 fracsqrt[3]1+2x+1sqrt2+x + x$
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I'm trying to solve this limit. Wolfram showed, that there's no limit, but I can clearly see that the limit exists from graph. Tried L'Hopital's rule, but didn't get any further.
$$lim_xto-1 fracsqrt[3]1+2x+1sqrt2+x + x$$
I don't know which method should I use
limits
 |Â
show 3 more comments
up vote
1
down vote
favorite
I'm trying to solve this limit. Wolfram showed, that there's no limit, but I can clearly see that the limit exists from graph. Tried L'Hopital's rule, but didn't get any further.
$$lim_xto-1 fracsqrt[3]1+2x+1sqrt2+x + x$$
I don't know which method should I use
limits
what limit do you see on the graph?
â Rushabh Mehta
Oct 3 at 21:29
@RushabhMehta, I made graph in google, so I can't say exactly, but it's around 0.4
â Narek Maloyan
Oct 3 at 21:32
Could you link the graph in the comments? I am intrigued
â Rushabh Mehta
Oct 3 at 21:32
@RushabhMehta, it should show google.com/â¦
â Narek Maloyan
Oct 3 at 21:34
Well, Google is being really weird I guess. That's not even close to the actual graph of the function. This is closer.
â Rushabh Mehta
Oct 3 at 21:37
 |Â
show 3 more comments
up vote
1
down vote
favorite
up vote
1
down vote
favorite
I'm trying to solve this limit. Wolfram showed, that there's no limit, but I can clearly see that the limit exists from graph. Tried L'Hopital's rule, but didn't get any further.
$$lim_xto-1 fracsqrt[3]1+2x+1sqrt2+x + x$$
I don't know which method should I use
limits
I'm trying to solve this limit. Wolfram showed, that there's no limit, but I can clearly see that the limit exists from graph. Tried L'Hopital's rule, but didn't get any further.
$$lim_xto-1 fracsqrt[3]1+2x+1sqrt2+x + x$$
I don't know which method should I use
limits
limits
edited Oct 4 at 0:00
Asaf Karagilaâ¦
296k32412739
296k32412739
asked Oct 3 at 21:24
Narek Maloyan
477312
477312
what limit do you see on the graph?
â Rushabh Mehta
Oct 3 at 21:29
@RushabhMehta, I made graph in google, so I can't say exactly, but it's around 0.4
â Narek Maloyan
Oct 3 at 21:32
Could you link the graph in the comments? I am intrigued
â Rushabh Mehta
Oct 3 at 21:32
@RushabhMehta, it should show google.com/â¦
â Narek Maloyan
Oct 3 at 21:34
Well, Google is being really weird I guess. That's not even close to the actual graph of the function. This is closer.
â Rushabh Mehta
Oct 3 at 21:37
 |Â
show 3 more comments
what limit do you see on the graph?
â Rushabh Mehta
Oct 3 at 21:29
@RushabhMehta, I made graph in google, so I can't say exactly, but it's around 0.4
â Narek Maloyan
Oct 3 at 21:32
Could you link the graph in the comments? I am intrigued
â Rushabh Mehta
Oct 3 at 21:32
@RushabhMehta, it should show google.com/â¦
â Narek Maloyan
Oct 3 at 21:34
Well, Google is being really weird I guess. That's not even close to the actual graph of the function. This is closer.
â Rushabh Mehta
Oct 3 at 21:37
what limit do you see on the graph?
â Rushabh Mehta
Oct 3 at 21:29
what limit do you see on the graph?
â Rushabh Mehta
Oct 3 at 21:29
@RushabhMehta, I made graph in google, so I can't say exactly, but it's around 0.4
â Narek Maloyan
Oct 3 at 21:32
@RushabhMehta, I made graph in google, so I can't say exactly, but it's around 0.4
â Narek Maloyan
Oct 3 at 21:32
Could you link the graph in the comments? I am intrigued
â Rushabh Mehta
Oct 3 at 21:32
Could you link the graph in the comments? I am intrigued
â Rushabh Mehta
Oct 3 at 21:32
@RushabhMehta, it should show google.com/â¦
â Narek Maloyan
Oct 3 at 21:34
@RushabhMehta, it should show google.com/â¦
â Narek Maloyan
Oct 3 at 21:34
Well, Google is being really weird I guess. That's not even close to the actual graph of the function. This is closer.
â Rushabh Mehta
Oct 3 at 21:37
Well, Google is being really weird I guess. That's not even close to the actual graph of the function. This is closer.
â Rushabh Mehta
Oct 3 at 21:37
 |Â
show 3 more comments
3 Answers
3
active
oldest
votes
up vote
3
down vote
accepted
Set $x=-1+h;$ ($hto 0$) and use the binomial approximation:
$sqrt[3]1+2(-1+h)+1=1-sqrt[3]1-2h=1-bigl(1-frac23 h+o(h)bigl)=frac23 h+o(h)$,
$sqrt2+(-1+h)-1+h=sqrt1+h-1+h=1+frac12h+o(h)-1+h=frac32h+o(h),$
so $;dfracsqrt[3]1+2x+1sqrt2+x + x=dfracfrac23 h+o(h)frac32h+o(h))=dfracfrac23+o(1)frac32+o(1)=dfrac49+o(1).$
add a comment |Â
up vote
5
down vote
Recall the formulas:
$$
beginalign
a^2 -b^2 &= (a - b)(a + b)\
a^3 + b^3 &= (a + b)(a^2 - ab + b^2)
endalign
$$
Using them we can get the following:
$$
beginalign
sqrt[3]1+2x + 1 &=
frac1 + 2x + 1sqrt[3]1+2x^2 - sqrt[3]1+2x + 1 =
frac2(x + 1)sqrt[3]1+2x^2 - sqrt[3]1+2x + 1 \
sqrt2+x + x &=
frac2 + x - x^2sqrt2+x - x =
-frac(x + 1)(x - 2)sqrt2+x - x
endalign
$$
Therefore, your limit is equal to
$$
lim_xto-1 fracsqrt[3]1+2x+1sqrt2+x + x =
lim_xto-1 -frac2(sqrt2+x - x)(x - 2)(sqrt[3]1+2x^2 - sqrt[3]1+2x + 1),
$$
which is pretty straightforward to compute.
That's beautiful
â Narek Maloyan
Oct 3 at 21:57
add a comment |Â
up vote
3
down vote
L'Hospital works:
$$lim_xto-1 fracsqrt[3]1+2x+1sqrt2+x + x=lim_xto-1 fracdfrac23(sqrt[3]1+2x)^2dfrac12sqrt2+x + 1=frac49.$$
add a comment |Â
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
3
down vote
accepted
Set $x=-1+h;$ ($hto 0$) and use the binomial approximation:
$sqrt[3]1+2(-1+h)+1=1-sqrt[3]1-2h=1-bigl(1-frac23 h+o(h)bigl)=frac23 h+o(h)$,
$sqrt2+(-1+h)-1+h=sqrt1+h-1+h=1+frac12h+o(h)-1+h=frac32h+o(h),$
so $;dfracsqrt[3]1+2x+1sqrt2+x + x=dfracfrac23 h+o(h)frac32h+o(h))=dfracfrac23+o(1)frac32+o(1)=dfrac49+o(1).$
add a comment |Â
up vote
3
down vote
accepted
Set $x=-1+h;$ ($hto 0$) and use the binomial approximation:
$sqrt[3]1+2(-1+h)+1=1-sqrt[3]1-2h=1-bigl(1-frac23 h+o(h)bigl)=frac23 h+o(h)$,
$sqrt2+(-1+h)-1+h=sqrt1+h-1+h=1+frac12h+o(h)-1+h=frac32h+o(h),$
so $;dfracsqrt[3]1+2x+1sqrt2+x + x=dfracfrac23 h+o(h)frac32h+o(h))=dfracfrac23+o(1)frac32+o(1)=dfrac49+o(1).$
add a comment |Â
up vote
3
down vote
accepted
up vote
3
down vote
accepted
Set $x=-1+h;$ ($hto 0$) and use the binomial approximation:
$sqrt[3]1+2(-1+h)+1=1-sqrt[3]1-2h=1-bigl(1-frac23 h+o(h)bigl)=frac23 h+o(h)$,
$sqrt2+(-1+h)-1+h=sqrt1+h-1+h=1+frac12h+o(h)-1+h=frac32h+o(h),$
so $;dfracsqrt[3]1+2x+1sqrt2+x + x=dfracfrac23 h+o(h)frac32h+o(h))=dfracfrac23+o(1)frac32+o(1)=dfrac49+o(1).$
Set $x=-1+h;$ ($hto 0$) and use the binomial approximation:
$sqrt[3]1+2(-1+h)+1=1-sqrt[3]1-2h=1-bigl(1-frac23 h+o(h)bigl)=frac23 h+o(h)$,
$sqrt2+(-1+h)-1+h=sqrt1+h-1+h=1+frac12h+o(h)-1+h=frac32h+o(h),$
so $;dfracsqrt[3]1+2x+1sqrt2+x + x=dfracfrac23 h+o(h)frac32h+o(h))=dfracfrac23+o(1)frac32+o(1)=dfrac49+o(1).$
answered Oct 3 at 21:39
Bernard
113k636104
113k636104
add a comment |Â
add a comment |Â
up vote
5
down vote
Recall the formulas:
$$
beginalign
a^2 -b^2 &= (a - b)(a + b)\
a^3 + b^3 &= (a + b)(a^2 - ab + b^2)
endalign
$$
Using them we can get the following:
$$
beginalign
sqrt[3]1+2x + 1 &=
frac1 + 2x + 1sqrt[3]1+2x^2 - sqrt[3]1+2x + 1 =
frac2(x + 1)sqrt[3]1+2x^2 - sqrt[3]1+2x + 1 \
sqrt2+x + x &=
frac2 + x - x^2sqrt2+x - x =
-frac(x + 1)(x - 2)sqrt2+x - x
endalign
$$
Therefore, your limit is equal to
$$
lim_xto-1 fracsqrt[3]1+2x+1sqrt2+x + x =
lim_xto-1 -frac2(sqrt2+x - x)(x - 2)(sqrt[3]1+2x^2 - sqrt[3]1+2x + 1),
$$
which is pretty straightforward to compute.
That's beautiful
â Narek Maloyan
Oct 3 at 21:57
add a comment |Â
up vote
5
down vote
Recall the formulas:
$$
beginalign
a^2 -b^2 &= (a - b)(a + b)\
a^3 + b^3 &= (a + b)(a^2 - ab + b^2)
endalign
$$
Using them we can get the following:
$$
beginalign
sqrt[3]1+2x + 1 &=
frac1 + 2x + 1sqrt[3]1+2x^2 - sqrt[3]1+2x + 1 =
frac2(x + 1)sqrt[3]1+2x^2 - sqrt[3]1+2x + 1 \
sqrt2+x + x &=
frac2 + x - x^2sqrt2+x - x =
-frac(x + 1)(x - 2)sqrt2+x - x
endalign
$$
Therefore, your limit is equal to
$$
lim_xto-1 fracsqrt[3]1+2x+1sqrt2+x + x =
lim_xto-1 -frac2(sqrt2+x - x)(x - 2)(sqrt[3]1+2x^2 - sqrt[3]1+2x + 1),
$$
which is pretty straightforward to compute.
That's beautiful
â Narek Maloyan
Oct 3 at 21:57
add a comment |Â
up vote
5
down vote
up vote
5
down vote
Recall the formulas:
$$
beginalign
a^2 -b^2 &= (a - b)(a + b)\
a^3 + b^3 &= (a + b)(a^2 - ab + b^2)
endalign
$$
Using them we can get the following:
$$
beginalign
sqrt[3]1+2x + 1 &=
frac1 + 2x + 1sqrt[3]1+2x^2 - sqrt[3]1+2x + 1 =
frac2(x + 1)sqrt[3]1+2x^2 - sqrt[3]1+2x + 1 \
sqrt2+x + x &=
frac2 + x - x^2sqrt2+x - x =
-frac(x + 1)(x - 2)sqrt2+x - x
endalign
$$
Therefore, your limit is equal to
$$
lim_xto-1 fracsqrt[3]1+2x+1sqrt2+x + x =
lim_xto-1 -frac2(sqrt2+x - x)(x - 2)(sqrt[3]1+2x^2 - sqrt[3]1+2x + 1),
$$
which is pretty straightforward to compute.
Recall the formulas:
$$
beginalign
a^2 -b^2 &= (a - b)(a + b)\
a^3 + b^3 &= (a + b)(a^2 - ab + b^2)
endalign
$$
Using them we can get the following:
$$
beginalign
sqrt[3]1+2x + 1 &=
frac1 + 2x + 1sqrt[3]1+2x^2 - sqrt[3]1+2x + 1 =
frac2(x + 1)sqrt[3]1+2x^2 - sqrt[3]1+2x + 1 \
sqrt2+x + x &=
frac2 + x - x^2sqrt2+x - x =
-frac(x + 1)(x - 2)sqrt2+x - x
endalign
$$
Therefore, your limit is equal to
$$
lim_xto-1 fracsqrt[3]1+2x+1sqrt2+x + x =
lim_xto-1 -frac2(sqrt2+x - x)(x - 2)(sqrt[3]1+2x^2 - sqrt[3]1+2x + 1),
$$
which is pretty straightforward to compute.
answered Oct 3 at 21:55
mwt
913116
913116
That's beautiful
â Narek Maloyan
Oct 3 at 21:57
add a comment |Â
That's beautiful
â Narek Maloyan
Oct 3 at 21:57
That's beautiful
â Narek Maloyan
Oct 3 at 21:57
That's beautiful
â Narek Maloyan
Oct 3 at 21:57
add a comment |Â
up vote
3
down vote
L'Hospital works:
$$lim_xto-1 fracsqrt[3]1+2x+1sqrt2+x + x=lim_xto-1 fracdfrac23(sqrt[3]1+2x)^2dfrac12sqrt2+x + 1=frac49.$$
add a comment |Â
up vote
3
down vote
L'Hospital works:
$$lim_xto-1 fracsqrt[3]1+2x+1sqrt2+x + x=lim_xto-1 fracdfrac23(sqrt[3]1+2x)^2dfrac12sqrt2+x + 1=frac49.$$
add a comment |Â
up vote
3
down vote
up vote
3
down vote
L'Hospital works:
$$lim_xto-1 fracsqrt[3]1+2x+1sqrt2+x + x=lim_xto-1 fracdfrac23(sqrt[3]1+2x)^2dfrac12sqrt2+x + 1=frac49.$$
L'Hospital works:
$$lim_xto-1 fracsqrt[3]1+2x+1sqrt2+x + x=lim_xto-1 fracdfrac23(sqrt[3]1+2x)^2dfrac12sqrt2+x + 1=frac49.$$
answered Oct 3 at 22:08
Yves Daoust
117k667213
117k667213
add a comment |Â
add a comment |Â
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what limit do you see on the graph?
â Rushabh Mehta
Oct 3 at 21:29
@RushabhMehta, I made graph in google, so I can't say exactly, but it's around 0.4
â Narek Maloyan
Oct 3 at 21:32
Could you link the graph in the comments? I am intrigued
â Rushabh Mehta
Oct 3 at 21:32
@RushabhMehta, it should show google.com/â¦
â Narek Maloyan
Oct 3 at 21:34
Well, Google is being really weird I guess. That's not even close to the actual graph of the function. This is closer.
â Rushabh Mehta
Oct 3 at 21:37