Does the value of the $lim_{x to 0-} x^x = 1$?
$begingroup$
I have the following attempt.
Let $x=-y$ then ${y to 0+}$ as ${x to 0-}$.
So, $displaystylelim_{x to 0-} {x}^{x}$= $displaystylelim_{y to 0+} {(-y)}^{(-y)} = displaystylelim_{y to 0+} dfrac{1}{{(-y)}^{y}}= displaystylelim_{y to 0+} dfrac{1}{{(-1)}^{y}.{y}^{y}}=displaystylelim_{y to 0+} dfrac{1}{{y}^{y}}$
Now as, $displaystylelim_{y to 0+} y^y =displaystylelim_{y to 0+} {e}^{yln{y}}
= {e}^{displaystylelim_{y to 0+} yln{y}}={e}^{displaystylelim_{y to 0+} frac{ln{y}}{frac{1}{y}}} = {e}^{displaystylelim_{y to 0+} frac{frac{1}{y}}{{-frac{1}{y^2}}}}
= {e}^{displaystylelim_{y to 0+} {-y}}=e^{0}=1$
Hence $displaystylelim_{y to 0+} dfrac{1}{{y}^{y}}=dfrac{1}{1}=1$
So, $displaystylelim_{x to 0-} {x}^{x}=1$
Is it correct?
complex-analysis limits
$endgroup$
|
show 1 more comment
$begingroup$
I have the following attempt.
Let $x=-y$ then ${y to 0+}$ as ${x to 0-}$.
So, $displaystylelim_{x to 0-} {x}^{x}$= $displaystylelim_{y to 0+} {(-y)}^{(-y)} = displaystylelim_{y to 0+} dfrac{1}{{(-y)}^{y}}= displaystylelim_{y to 0+} dfrac{1}{{(-1)}^{y}.{y}^{y}}=displaystylelim_{y to 0+} dfrac{1}{{y}^{y}}$
Now as, $displaystylelim_{y to 0+} y^y =displaystylelim_{y to 0+} {e}^{yln{y}}
= {e}^{displaystylelim_{y to 0+} yln{y}}={e}^{displaystylelim_{y to 0+} frac{ln{y}}{frac{1}{y}}} = {e}^{displaystylelim_{y to 0+} frac{frac{1}{y}}{{-frac{1}{y^2}}}}
= {e}^{displaystylelim_{y to 0+} {-y}}=e^{0}=1$
Hence $displaystylelim_{y to 0+} dfrac{1}{{y}^{y}}=dfrac{1}{1}=1$
So, $displaystylelim_{x to 0-} {x}^{x}=1$
Is it correct?
complex-analysis limits
$endgroup$
$begingroup$
For the term $$x^x$$ must be $$x>0$$ in the other case we get a complex number.
$endgroup$
– Dr. Sonnhard Graubner
Dec 24 '18 at 15:32
1
$begingroup$
How did you write $left( -1 right)^y = 1$? Don't you think if we take a sequence $dfrac{1}{n}$, $left( -1 right)^{frac{1}{n}}$ may not be defined in $mathbb{R}$?
$endgroup$
– Aniruddha Deshmukh
Dec 24 '18 at 15:32
2
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It depends on your definition of $a^b$ for $a<0$, but using $a^b=e^{b(ln(-a)+pi i)}$ your argument should work.
$endgroup$
– SmileyCraft
Dec 24 '18 at 15:33
1
$begingroup$
$x^y$ is not defined if$x<0$ and$y$ is not an integer.
$endgroup$
– Bernard
Dec 24 '18 at 15:40
$begingroup$
Are you trying to typeset limits from above/below? Just want to be sure before I edit with corrected LaTeX.
$endgroup$
– The Pointer
Dec 24 '18 at 15:57
|
show 1 more comment
$begingroup$
I have the following attempt.
Let $x=-y$ then ${y to 0+}$ as ${x to 0-}$.
So, $displaystylelim_{x to 0-} {x}^{x}$= $displaystylelim_{y to 0+} {(-y)}^{(-y)} = displaystylelim_{y to 0+} dfrac{1}{{(-y)}^{y}}= displaystylelim_{y to 0+} dfrac{1}{{(-1)}^{y}.{y}^{y}}=displaystylelim_{y to 0+} dfrac{1}{{y}^{y}}$
Now as, $displaystylelim_{y to 0+} y^y =displaystylelim_{y to 0+} {e}^{yln{y}}
= {e}^{displaystylelim_{y to 0+} yln{y}}={e}^{displaystylelim_{y to 0+} frac{ln{y}}{frac{1}{y}}} = {e}^{displaystylelim_{y to 0+} frac{frac{1}{y}}{{-frac{1}{y^2}}}}
= {e}^{displaystylelim_{y to 0+} {-y}}=e^{0}=1$
Hence $displaystylelim_{y to 0+} dfrac{1}{{y}^{y}}=dfrac{1}{1}=1$
So, $displaystylelim_{x to 0-} {x}^{x}=1$
Is it correct?
complex-analysis limits
$endgroup$
I have the following attempt.
Let $x=-y$ then ${y to 0+}$ as ${x to 0-}$.
So, $displaystylelim_{x to 0-} {x}^{x}$= $displaystylelim_{y to 0+} {(-y)}^{(-y)} = displaystylelim_{y to 0+} dfrac{1}{{(-y)}^{y}}= displaystylelim_{y to 0+} dfrac{1}{{(-1)}^{y}.{y}^{y}}=displaystylelim_{y to 0+} dfrac{1}{{y}^{y}}$
Now as, $displaystylelim_{y to 0+} y^y =displaystylelim_{y to 0+} {e}^{yln{y}}
= {e}^{displaystylelim_{y to 0+} yln{y}}={e}^{displaystylelim_{y to 0+} frac{ln{y}}{frac{1}{y}}} = {e}^{displaystylelim_{y to 0+} frac{frac{1}{y}}{{-frac{1}{y^2}}}}
= {e}^{displaystylelim_{y to 0+} {-y}}=e^{0}=1$
Hence $displaystylelim_{y to 0+} dfrac{1}{{y}^{y}}=dfrac{1}{1}=1$
So, $displaystylelim_{x to 0-} {x}^{x}=1$
Is it correct?
complex-analysis limits
complex-analysis limits
edited Dec 24 '18 at 15:45
Kousik Sett
asked Dec 24 '18 at 15:30
Kousik SettKousik Sett
1026
1026
$begingroup$
For the term $$x^x$$ must be $$x>0$$ in the other case we get a complex number.
$endgroup$
– Dr. Sonnhard Graubner
Dec 24 '18 at 15:32
1
$begingroup$
How did you write $left( -1 right)^y = 1$? Don't you think if we take a sequence $dfrac{1}{n}$, $left( -1 right)^{frac{1}{n}}$ may not be defined in $mathbb{R}$?
$endgroup$
– Aniruddha Deshmukh
Dec 24 '18 at 15:32
2
$begingroup$
It depends on your definition of $a^b$ for $a<0$, but using $a^b=e^{b(ln(-a)+pi i)}$ your argument should work.
$endgroup$
– SmileyCraft
Dec 24 '18 at 15:33
1
$begingroup$
$x^y$ is not defined if$x<0$ and$y$ is not an integer.
$endgroup$
– Bernard
Dec 24 '18 at 15:40
$begingroup$
Are you trying to typeset limits from above/below? Just want to be sure before I edit with corrected LaTeX.
$endgroup$
– The Pointer
Dec 24 '18 at 15:57
|
show 1 more comment
$begingroup$
For the term $$x^x$$ must be $$x>0$$ in the other case we get a complex number.
$endgroup$
– Dr. Sonnhard Graubner
Dec 24 '18 at 15:32
1
$begingroup$
How did you write $left( -1 right)^y = 1$? Don't you think if we take a sequence $dfrac{1}{n}$, $left( -1 right)^{frac{1}{n}}$ may not be defined in $mathbb{R}$?
$endgroup$
– Aniruddha Deshmukh
Dec 24 '18 at 15:32
2
$begingroup$
It depends on your definition of $a^b$ for $a<0$, but using $a^b=e^{b(ln(-a)+pi i)}$ your argument should work.
$endgroup$
– SmileyCraft
Dec 24 '18 at 15:33
1
$begingroup$
$x^y$ is not defined if$x<0$ and$y$ is not an integer.
$endgroup$
– Bernard
Dec 24 '18 at 15:40
$begingroup$
Are you trying to typeset limits from above/below? Just want to be sure before I edit with corrected LaTeX.
$endgroup$
– The Pointer
Dec 24 '18 at 15:57
$begingroup$
For the term $$x^x$$ must be $$x>0$$ in the other case we get a complex number.
$endgroup$
– Dr. Sonnhard Graubner
Dec 24 '18 at 15:32
$begingroup$
For the term $$x^x$$ must be $$x>0$$ in the other case we get a complex number.
$endgroup$
– Dr. Sonnhard Graubner
Dec 24 '18 at 15:32
1
1
$begingroup$
How did you write $left( -1 right)^y = 1$? Don't you think if we take a sequence $dfrac{1}{n}$, $left( -1 right)^{frac{1}{n}}$ may not be defined in $mathbb{R}$?
$endgroup$
– Aniruddha Deshmukh
Dec 24 '18 at 15:32
$begingroup$
How did you write $left( -1 right)^y = 1$? Don't you think if we take a sequence $dfrac{1}{n}$, $left( -1 right)^{frac{1}{n}}$ may not be defined in $mathbb{R}$?
$endgroup$
– Aniruddha Deshmukh
Dec 24 '18 at 15:32
2
2
$begingroup$
It depends on your definition of $a^b$ for $a<0$, but using $a^b=e^{b(ln(-a)+pi i)}$ your argument should work.
$endgroup$
– SmileyCraft
Dec 24 '18 at 15:33
$begingroup$
It depends on your definition of $a^b$ for $a<0$, but using $a^b=e^{b(ln(-a)+pi i)}$ your argument should work.
$endgroup$
– SmileyCraft
Dec 24 '18 at 15:33
1
1
$begingroup$
$x^y$ is not defined if$x<0$ and$y$ is not an integer.
$endgroup$
– Bernard
Dec 24 '18 at 15:40
$begingroup$
$x^y$ is not defined if$x<0$ and$y$ is not an integer.
$endgroup$
– Bernard
Dec 24 '18 at 15:40
$begingroup$
Are you trying to typeset limits from above/below? Just want to be sure before I edit with corrected LaTeX.
$endgroup$
– The Pointer
Dec 24 '18 at 15:57
$begingroup$
Are you trying to typeset limits from above/below? Just want to be sure before I edit with corrected LaTeX.
$endgroup$
– The Pointer
Dec 24 '18 at 15:57
|
show 1 more comment
2 Answers
2
active
oldest
votes
$begingroup$
For complex values of $z$ and $w$, we have by definition
$$begin{align}
z^w&=e^{wlog(z)}\\
&=e^{wtext{Log}(|z|)+iwarg(z)}tag1
end{align}$$
where $text{Log}$ is the logarithm function of real variables and $arg(z)$ is the multi-valued argument of $z$.
Using $(1)$ reveals for $xin mathbb{R}$ and $x<0$
$$begin{align}
lim_{xto 0^-}x^x&=lim_{xto 0^-}e^{xtext{Log}(|x|)+ixarg(x)}\\
&=lim_{xto 0^-}x^{|x|}e^{ix(2n+1)pi}\\
&=1
end{align}$$
as was to be shown!
$endgroup$
add a comment |
$begingroup$
Let $x<0$. It holds that $x^x=e^{xlog x} = e^{x (log(-x)+pi i)} = e^{xlog(-x)}(cos(pi x) + i sin (pi x))$. And I think you can complete the details.
$endgroup$
$begingroup$
Note that for $x<0$, $log(x)=text{Log}(|x|)+i(2n+1)pi$, for $nin mathbb{Z}$.
$endgroup$
– Mark Viola
Dec 24 '18 at 16:17
add a comment |
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2 Answers
2
active
oldest
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2 Answers
2
active
oldest
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$begingroup$
For complex values of $z$ and $w$, we have by definition
$$begin{align}
z^w&=e^{wlog(z)}\\
&=e^{wtext{Log}(|z|)+iwarg(z)}tag1
end{align}$$
where $text{Log}$ is the logarithm function of real variables and $arg(z)$ is the multi-valued argument of $z$.
Using $(1)$ reveals for $xin mathbb{R}$ and $x<0$
$$begin{align}
lim_{xto 0^-}x^x&=lim_{xto 0^-}e^{xtext{Log}(|x|)+ixarg(x)}\\
&=lim_{xto 0^-}x^{|x|}e^{ix(2n+1)pi}\\
&=1
end{align}$$
as was to be shown!
$endgroup$
add a comment |
$begingroup$
For complex values of $z$ and $w$, we have by definition
$$begin{align}
z^w&=e^{wlog(z)}\\
&=e^{wtext{Log}(|z|)+iwarg(z)}tag1
end{align}$$
where $text{Log}$ is the logarithm function of real variables and $arg(z)$ is the multi-valued argument of $z$.
Using $(1)$ reveals for $xin mathbb{R}$ and $x<0$
$$begin{align}
lim_{xto 0^-}x^x&=lim_{xto 0^-}e^{xtext{Log}(|x|)+ixarg(x)}\\
&=lim_{xto 0^-}x^{|x|}e^{ix(2n+1)pi}\\
&=1
end{align}$$
as was to be shown!
$endgroup$
add a comment |
$begingroup$
For complex values of $z$ and $w$, we have by definition
$$begin{align}
z^w&=e^{wlog(z)}\\
&=e^{wtext{Log}(|z|)+iwarg(z)}tag1
end{align}$$
where $text{Log}$ is the logarithm function of real variables and $arg(z)$ is the multi-valued argument of $z$.
Using $(1)$ reveals for $xin mathbb{R}$ and $x<0$
$$begin{align}
lim_{xto 0^-}x^x&=lim_{xto 0^-}e^{xtext{Log}(|x|)+ixarg(x)}\\
&=lim_{xto 0^-}x^{|x|}e^{ix(2n+1)pi}\\
&=1
end{align}$$
as was to be shown!
$endgroup$
For complex values of $z$ and $w$, we have by definition
$$begin{align}
z^w&=e^{wlog(z)}\\
&=e^{wtext{Log}(|z|)+iwarg(z)}tag1
end{align}$$
where $text{Log}$ is the logarithm function of real variables and $arg(z)$ is the multi-valued argument of $z$.
Using $(1)$ reveals for $xin mathbb{R}$ and $x<0$
$$begin{align}
lim_{xto 0^-}x^x&=lim_{xto 0^-}e^{xtext{Log}(|x|)+ixarg(x)}\\
&=lim_{xto 0^-}x^{|x|}e^{ix(2n+1)pi}\\
&=1
end{align}$$
as was to be shown!
answered Dec 24 '18 at 16:14
Mark ViolaMark Viola
134k1278177
134k1278177
add a comment |
add a comment |
$begingroup$
Let $x<0$. It holds that $x^x=e^{xlog x} = e^{x (log(-x)+pi i)} = e^{xlog(-x)}(cos(pi x) + i sin (pi x))$. And I think you can complete the details.
$endgroup$
$begingroup$
Note that for $x<0$, $log(x)=text{Log}(|x|)+i(2n+1)pi$, for $nin mathbb{Z}$.
$endgroup$
– Mark Viola
Dec 24 '18 at 16:17
add a comment |
$begingroup$
Let $x<0$. It holds that $x^x=e^{xlog x} = e^{x (log(-x)+pi i)} = e^{xlog(-x)}(cos(pi x) + i sin (pi x))$. And I think you can complete the details.
$endgroup$
$begingroup$
Note that for $x<0$, $log(x)=text{Log}(|x|)+i(2n+1)pi$, for $nin mathbb{Z}$.
$endgroup$
– Mark Viola
Dec 24 '18 at 16:17
add a comment |
$begingroup$
Let $x<0$. It holds that $x^x=e^{xlog x} = e^{x (log(-x)+pi i)} = e^{xlog(-x)}(cos(pi x) + i sin (pi x))$. And I think you can complete the details.
$endgroup$
Let $x<0$. It holds that $x^x=e^{xlog x} = e^{x (log(-x)+pi i)} = e^{xlog(-x)}(cos(pi x) + i sin (pi x))$. And I think you can complete the details.
answered Dec 24 '18 at 16:13
MirceaMircea
1736
1736
$begingroup$
Note that for $x<0$, $log(x)=text{Log}(|x|)+i(2n+1)pi$, for $nin mathbb{Z}$.
$endgroup$
– Mark Viola
Dec 24 '18 at 16:17
add a comment |
$begingroup$
Note that for $x<0$, $log(x)=text{Log}(|x|)+i(2n+1)pi$, for $nin mathbb{Z}$.
$endgroup$
– Mark Viola
Dec 24 '18 at 16:17
$begingroup$
Note that for $x<0$, $log(x)=text{Log}(|x|)+i(2n+1)pi$, for $nin mathbb{Z}$.
$endgroup$
– Mark Viola
Dec 24 '18 at 16:17
$begingroup$
Note that for $x<0$, $log(x)=text{Log}(|x|)+i(2n+1)pi$, for $nin mathbb{Z}$.
$endgroup$
– Mark Viola
Dec 24 '18 at 16:17
add a comment |
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$begingroup$
For the term $$x^x$$ must be $$x>0$$ in the other case we get a complex number.
$endgroup$
– Dr. Sonnhard Graubner
Dec 24 '18 at 15:32
1
$begingroup$
How did you write $left( -1 right)^y = 1$? Don't you think if we take a sequence $dfrac{1}{n}$, $left( -1 right)^{frac{1}{n}}$ may not be defined in $mathbb{R}$?
$endgroup$
– Aniruddha Deshmukh
Dec 24 '18 at 15:32
2
$begingroup$
It depends on your definition of $a^b$ for $a<0$, but using $a^b=e^{b(ln(-a)+pi i)}$ your argument should work.
$endgroup$
– SmileyCraft
Dec 24 '18 at 15:33
1
$begingroup$
$x^y$ is not defined if$x<0$ and$y$ is not an integer.
$endgroup$
– Bernard
Dec 24 '18 at 15:40
$begingroup$
Are you trying to typeset limits from above/below? Just want to be sure before I edit with corrected LaTeX.
$endgroup$
– The Pointer
Dec 24 '18 at 15:57