Is $1 / sqrt{x}$ Riemann integrable on $[0,1]$?
up vote
2
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If $int_0^1 1 / sqrt{x}$ Riemann integrable then using second fundamental theorem of calculus i can easily say that $sqrt{x}$ is uniformly continuous.
Basically it has one point i.e $0$ where it diverges .Otherwise i can use the theorem that a function with finite number of discontinuous points is Riemann integrable. Can i take zero as point of discontinuity ?
real-analysis riemann-integration
add a comment |
up vote
2
down vote
favorite
If $int_0^1 1 / sqrt{x}$ Riemann integrable then using second fundamental theorem of calculus i can easily say that $sqrt{x}$ is uniformly continuous.
Basically it has one point i.e $0$ where it diverges .Otherwise i can use the theorem that a function with finite number of discontinuous points is Riemann integrable. Can i take zero as point of discontinuity ?
real-analysis riemann-integration
2
Is $dfrac{1}{sqrt{x}}$ bounded at $x=0$?
– Yadati Kiran
Nov 27 at 13:11
3
$sqrt x$ is continuous on the compact interval $[0, 1]$ – that already implies uniform continuity on the interval. You don't need an integral for that argument.
– Martin R
Nov 27 at 13:13
1
Note that $sqrt{x}$ is uniformly continuous on all of $mathbb{R}^{+}$. math.stackexchange.com/questions/569928/…
– Euler....IS_ALIVE
Nov 27 at 13:14
2
Looks like an XY problem ...
– Martin R
Nov 27 at 13:16
@MartinR No .X was my main problem i just stated Y (Y can be solved by this way also )
– Amit
Nov 27 at 13:18
add a comment |
up vote
2
down vote
favorite
up vote
2
down vote
favorite
If $int_0^1 1 / sqrt{x}$ Riemann integrable then using second fundamental theorem of calculus i can easily say that $sqrt{x}$ is uniformly continuous.
Basically it has one point i.e $0$ where it diverges .Otherwise i can use the theorem that a function with finite number of discontinuous points is Riemann integrable. Can i take zero as point of discontinuity ?
real-analysis riemann-integration
If $int_0^1 1 / sqrt{x}$ Riemann integrable then using second fundamental theorem of calculus i can easily say that $sqrt{x}$ is uniformly continuous.
Basically it has one point i.e $0$ where it diverges .Otherwise i can use the theorem that a function with finite number of discontinuous points is Riemann integrable. Can i take zero as point of discontinuity ?
real-analysis riemann-integration
real-analysis riemann-integration
edited Nov 27 at 13:13
asked Nov 27 at 13:09
Amit
1398
1398
2
Is $dfrac{1}{sqrt{x}}$ bounded at $x=0$?
– Yadati Kiran
Nov 27 at 13:11
3
$sqrt x$ is continuous on the compact interval $[0, 1]$ – that already implies uniform continuity on the interval. You don't need an integral for that argument.
– Martin R
Nov 27 at 13:13
1
Note that $sqrt{x}$ is uniformly continuous on all of $mathbb{R}^{+}$. math.stackexchange.com/questions/569928/…
– Euler....IS_ALIVE
Nov 27 at 13:14
2
Looks like an XY problem ...
– Martin R
Nov 27 at 13:16
@MartinR No .X was my main problem i just stated Y (Y can be solved by this way also )
– Amit
Nov 27 at 13:18
add a comment |
2
Is $dfrac{1}{sqrt{x}}$ bounded at $x=0$?
– Yadati Kiran
Nov 27 at 13:11
3
$sqrt x$ is continuous on the compact interval $[0, 1]$ – that already implies uniform continuity on the interval. You don't need an integral for that argument.
– Martin R
Nov 27 at 13:13
1
Note that $sqrt{x}$ is uniformly continuous on all of $mathbb{R}^{+}$. math.stackexchange.com/questions/569928/…
– Euler....IS_ALIVE
Nov 27 at 13:14
2
Looks like an XY problem ...
– Martin R
Nov 27 at 13:16
@MartinR No .X was my main problem i just stated Y (Y can be solved by this way also )
– Amit
Nov 27 at 13:18
2
2
Is $dfrac{1}{sqrt{x}}$ bounded at $x=0$?
– Yadati Kiran
Nov 27 at 13:11
Is $dfrac{1}{sqrt{x}}$ bounded at $x=0$?
– Yadati Kiran
Nov 27 at 13:11
3
3
$sqrt x$ is continuous on the compact interval $[0, 1]$ – that already implies uniform continuity on the interval. You don't need an integral for that argument.
– Martin R
Nov 27 at 13:13
$sqrt x$ is continuous on the compact interval $[0, 1]$ – that already implies uniform continuity on the interval. You don't need an integral for that argument.
– Martin R
Nov 27 at 13:13
1
1
Note that $sqrt{x}$ is uniformly continuous on all of $mathbb{R}^{+}$. math.stackexchange.com/questions/569928/…
– Euler....IS_ALIVE
Nov 27 at 13:14
Note that $sqrt{x}$ is uniformly continuous on all of $mathbb{R}^{+}$. math.stackexchange.com/questions/569928/…
– Euler....IS_ALIVE
Nov 27 at 13:14
2
2
Looks like an XY problem ...
– Martin R
Nov 27 at 13:16
Looks like an XY problem ...
– Martin R
Nov 27 at 13:16
@MartinR No .X was my main problem i just stated Y (Y can be solved by this way also )
– Amit
Nov 27 at 13:18
@MartinR No .X was my main problem i just stated Y (Y can be solved by this way also )
– Amit
Nov 27 at 13:18
add a comment |
4 Answers
4
active
oldest
votes
up vote
5
down vote
accepted
That function is unbounded (whatever way you chhose it to extend it to $0$), and therefore it is not Riemann-integrable (by definition, every Riemann-integrable function is bounded). However, the improper integral $int_0^1frac1{sqrt x},mathrm dx$ converges.
The theorem that you mentioned holds for bounded functions, not in general.
This means when we talk about Riemann integrable functions we mean that it has to be bounded ? in other words we consider only bounded functions in study of Riemann integration ?
– Amit
Nov 27 at 13:16
1
Yes, you are absolutely right.
– José Carlos Santos
Nov 27 at 13:18
Also one more doubt - suppose a function is unbounded at a point ( like the function in this question is unbounded at $0$ ) then can we say the function is discontinuous at that point ? (This doubt is irrelevant to this question)
– Amit
Nov 27 at 13:27
1
Yes, that is correct. To be more precise: if $a$ belongs to the domain $D_f$ of $f$ and if, for each $r>0$, the restriction of $f$ to $(a-r,a+r)cap D_f$ is unbounded, then $f$ is discontinuous at $a$.
– José Carlos Santos
Nov 27 at 13:30
add a comment |
up vote
3
down vote
$frac{1}{sqrt{x}}$ is not bounded on $(0,1)$, and therefore, it cannot be Riemann integrable.
However, $sqrt{x}$ is continuous on $[0,1]$ and $[0,1]$ is a compact set, therefore, $sqrt x$ is uniformly continuous on $[0,1]$. Also, the derivative of $sqrt{x}$ is bounded on $[1, infty)$, so $sqrt{x}$ is uniformly continuous on $[1, infty)$.
add a comment |
up vote
2
down vote
It's unbounded so no it's not Riemann integrable. It is improperly Riemann integrable though.
add a comment |
up vote
2
down vote
The problem here is that the integrand is unbounded in the domain of integration so it is not Riemann integrable.
The improper integral does exist if it is perrceived as the limit $$displaystylelim_{ato0^+}int_a^1dfrac{1}{sqrt{x}}=lim_{ato0^+}(2-2sqrt{a})=2$$
add a comment |
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4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
5
down vote
accepted
That function is unbounded (whatever way you chhose it to extend it to $0$), and therefore it is not Riemann-integrable (by definition, every Riemann-integrable function is bounded). However, the improper integral $int_0^1frac1{sqrt x},mathrm dx$ converges.
The theorem that you mentioned holds for bounded functions, not in general.
This means when we talk about Riemann integrable functions we mean that it has to be bounded ? in other words we consider only bounded functions in study of Riemann integration ?
– Amit
Nov 27 at 13:16
1
Yes, you are absolutely right.
– José Carlos Santos
Nov 27 at 13:18
Also one more doubt - suppose a function is unbounded at a point ( like the function in this question is unbounded at $0$ ) then can we say the function is discontinuous at that point ? (This doubt is irrelevant to this question)
– Amit
Nov 27 at 13:27
1
Yes, that is correct. To be more precise: if $a$ belongs to the domain $D_f$ of $f$ and if, for each $r>0$, the restriction of $f$ to $(a-r,a+r)cap D_f$ is unbounded, then $f$ is discontinuous at $a$.
– José Carlos Santos
Nov 27 at 13:30
add a comment |
up vote
5
down vote
accepted
That function is unbounded (whatever way you chhose it to extend it to $0$), and therefore it is not Riemann-integrable (by definition, every Riemann-integrable function is bounded). However, the improper integral $int_0^1frac1{sqrt x},mathrm dx$ converges.
The theorem that you mentioned holds for bounded functions, not in general.
This means when we talk about Riemann integrable functions we mean that it has to be bounded ? in other words we consider only bounded functions in study of Riemann integration ?
– Amit
Nov 27 at 13:16
1
Yes, you are absolutely right.
– José Carlos Santos
Nov 27 at 13:18
Also one more doubt - suppose a function is unbounded at a point ( like the function in this question is unbounded at $0$ ) then can we say the function is discontinuous at that point ? (This doubt is irrelevant to this question)
– Amit
Nov 27 at 13:27
1
Yes, that is correct. To be more precise: if $a$ belongs to the domain $D_f$ of $f$ and if, for each $r>0$, the restriction of $f$ to $(a-r,a+r)cap D_f$ is unbounded, then $f$ is discontinuous at $a$.
– José Carlos Santos
Nov 27 at 13:30
add a comment |
up vote
5
down vote
accepted
up vote
5
down vote
accepted
That function is unbounded (whatever way you chhose it to extend it to $0$), and therefore it is not Riemann-integrable (by definition, every Riemann-integrable function is bounded). However, the improper integral $int_0^1frac1{sqrt x},mathrm dx$ converges.
The theorem that you mentioned holds for bounded functions, not in general.
That function is unbounded (whatever way you chhose it to extend it to $0$), and therefore it is not Riemann-integrable (by definition, every Riemann-integrable function is bounded). However, the improper integral $int_0^1frac1{sqrt x},mathrm dx$ converges.
The theorem that you mentioned holds for bounded functions, not in general.
answered Nov 27 at 13:11
José Carlos Santos
146k22116215
146k22116215
This means when we talk about Riemann integrable functions we mean that it has to be bounded ? in other words we consider only bounded functions in study of Riemann integration ?
– Amit
Nov 27 at 13:16
1
Yes, you are absolutely right.
– José Carlos Santos
Nov 27 at 13:18
Also one more doubt - suppose a function is unbounded at a point ( like the function in this question is unbounded at $0$ ) then can we say the function is discontinuous at that point ? (This doubt is irrelevant to this question)
– Amit
Nov 27 at 13:27
1
Yes, that is correct. To be more precise: if $a$ belongs to the domain $D_f$ of $f$ and if, for each $r>0$, the restriction of $f$ to $(a-r,a+r)cap D_f$ is unbounded, then $f$ is discontinuous at $a$.
– José Carlos Santos
Nov 27 at 13:30
add a comment |
This means when we talk about Riemann integrable functions we mean that it has to be bounded ? in other words we consider only bounded functions in study of Riemann integration ?
– Amit
Nov 27 at 13:16
1
Yes, you are absolutely right.
– José Carlos Santos
Nov 27 at 13:18
Also one more doubt - suppose a function is unbounded at a point ( like the function in this question is unbounded at $0$ ) then can we say the function is discontinuous at that point ? (This doubt is irrelevant to this question)
– Amit
Nov 27 at 13:27
1
Yes, that is correct. To be more precise: if $a$ belongs to the domain $D_f$ of $f$ and if, for each $r>0$, the restriction of $f$ to $(a-r,a+r)cap D_f$ is unbounded, then $f$ is discontinuous at $a$.
– José Carlos Santos
Nov 27 at 13:30
This means when we talk about Riemann integrable functions we mean that it has to be bounded ? in other words we consider only bounded functions in study of Riemann integration ?
– Amit
Nov 27 at 13:16
This means when we talk about Riemann integrable functions we mean that it has to be bounded ? in other words we consider only bounded functions in study of Riemann integration ?
– Amit
Nov 27 at 13:16
1
1
Yes, you are absolutely right.
– José Carlos Santos
Nov 27 at 13:18
Yes, you are absolutely right.
– José Carlos Santos
Nov 27 at 13:18
Also one more doubt - suppose a function is unbounded at a point ( like the function in this question is unbounded at $0$ ) then can we say the function is discontinuous at that point ? (This doubt is irrelevant to this question)
– Amit
Nov 27 at 13:27
Also one more doubt - suppose a function is unbounded at a point ( like the function in this question is unbounded at $0$ ) then can we say the function is discontinuous at that point ? (This doubt is irrelevant to this question)
– Amit
Nov 27 at 13:27
1
1
Yes, that is correct. To be more precise: if $a$ belongs to the domain $D_f$ of $f$ and if, for each $r>0$, the restriction of $f$ to $(a-r,a+r)cap D_f$ is unbounded, then $f$ is discontinuous at $a$.
– José Carlos Santos
Nov 27 at 13:30
Yes, that is correct. To be more precise: if $a$ belongs to the domain $D_f$ of $f$ and if, for each $r>0$, the restriction of $f$ to $(a-r,a+r)cap D_f$ is unbounded, then $f$ is discontinuous at $a$.
– José Carlos Santos
Nov 27 at 13:30
add a comment |
up vote
3
down vote
$frac{1}{sqrt{x}}$ is not bounded on $(0,1)$, and therefore, it cannot be Riemann integrable.
However, $sqrt{x}$ is continuous on $[0,1]$ and $[0,1]$ is a compact set, therefore, $sqrt x$ is uniformly continuous on $[0,1]$. Also, the derivative of $sqrt{x}$ is bounded on $[1, infty)$, so $sqrt{x}$ is uniformly continuous on $[1, infty)$.
add a comment |
up vote
3
down vote
$frac{1}{sqrt{x}}$ is not bounded on $(0,1)$, and therefore, it cannot be Riemann integrable.
However, $sqrt{x}$ is continuous on $[0,1]$ and $[0,1]$ is a compact set, therefore, $sqrt x$ is uniformly continuous on $[0,1]$. Also, the derivative of $sqrt{x}$ is bounded on $[1, infty)$, so $sqrt{x}$ is uniformly continuous on $[1, infty)$.
add a comment |
up vote
3
down vote
up vote
3
down vote
$frac{1}{sqrt{x}}$ is not bounded on $(0,1)$, and therefore, it cannot be Riemann integrable.
However, $sqrt{x}$ is continuous on $[0,1]$ and $[0,1]$ is a compact set, therefore, $sqrt x$ is uniformly continuous on $[0,1]$. Also, the derivative of $sqrt{x}$ is bounded on $[1, infty)$, so $sqrt{x}$ is uniformly continuous on $[1, infty)$.
$frac{1}{sqrt{x}}$ is not bounded on $(0,1)$, and therefore, it cannot be Riemann integrable.
However, $sqrt{x}$ is continuous on $[0,1]$ and $[0,1]$ is a compact set, therefore, $sqrt x$ is uniformly continuous on $[0,1]$. Also, the derivative of $sqrt{x}$ is bounded on $[1, infty)$, so $sqrt{x}$ is uniformly continuous on $[1, infty)$.
answered Nov 27 at 13:13
5xum
89.4k393161
89.4k393161
add a comment |
add a comment |
up vote
2
down vote
It's unbounded so no it's not Riemann integrable. It is improperly Riemann integrable though.
add a comment |
up vote
2
down vote
It's unbounded so no it's not Riemann integrable. It is improperly Riemann integrable though.
add a comment |
up vote
2
down vote
up vote
2
down vote
It's unbounded so no it's not Riemann integrable. It is improperly Riemann integrable though.
It's unbounded so no it's not Riemann integrable. It is improperly Riemann integrable though.
answered Nov 27 at 13:11
Zachary Selk
536311
536311
add a comment |
add a comment |
up vote
2
down vote
The problem here is that the integrand is unbounded in the domain of integration so it is not Riemann integrable.
The improper integral does exist if it is perrceived as the limit $$displaystylelim_{ato0^+}int_a^1dfrac{1}{sqrt{x}}=lim_{ato0^+}(2-2sqrt{a})=2$$
add a comment |
up vote
2
down vote
The problem here is that the integrand is unbounded in the domain of integration so it is not Riemann integrable.
The improper integral does exist if it is perrceived as the limit $$displaystylelim_{ato0^+}int_a^1dfrac{1}{sqrt{x}}=lim_{ato0^+}(2-2sqrt{a})=2$$
add a comment |
up vote
2
down vote
up vote
2
down vote
The problem here is that the integrand is unbounded in the domain of integration so it is not Riemann integrable.
The improper integral does exist if it is perrceived as the limit $$displaystylelim_{ato0^+}int_a^1dfrac{1}{sqrt{x}}=lim_{ato0^+}(2-2sqrt{a})=2$$
The problem here is that the integrand is unbounded in the domain of integration so it is not Riemann integrable.
The improper integral does exist if it is perrceived as the limit $$displaystylelim_{ato0^+}int_a^1dfrac{1}{sqrt{x}}=lim_{ato0^+}(2-2sqrt{a})=2$$
answered Nov 27 at 13:17
Yadati Kiran
1,327418
1,327418
add a comment |
add a comment |
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2
Is $dfrac{1}{sqrt{x}}$ bounded at $x=0$?
– Yadati Kiran
Nov 27 at 13:11
3
$sqrt x$ is continuous on the compact interval $[0, 1]$ – that already implies uniform continuity on the interval. You don't need an integral for that argument.
– Martin R
Nov 27 at 13:13
1
Note that $sqrt{x}$ is uniformly continuous on all of $mathbb{R}^{+}$. math.stackexchange.com/questions/569928/…
– Euler....IS_ALIVE
Nov 27 at 13:14
2
Looks like an XY problem ...
– Martin R
Nov 27 at 13:16
@MartinR No .X was my main problem i just stated Y (Y can be solved by this way also )
– Amit
Nov 27 at 13:18