How can I find y?
$begingroup$
The following equation is given: $$ye^y=e^{x+1}$$ when $x=0$. I tried to solve it as logarithmic equation but I can't go further. I know $y=1$ but I don't know how to prove it. Any idea? Thank you😊
exponential-function functional-equations
$endgroup$
add a comment |
$begingroup$
The following equation is given: $$ye^y=e^{x+1}$$ when $x=0$. I tried to solve it as logarithmic equation but I can't go further. I know $y=1$ but I don't know how to prove it. Any idea? Thank you😊
exponential-function functional-equations
$endgroup$
$begingroup$
Indeed, someone has thought if this problem before: en.wikipedia.org/wiki/Lambert_W_function
$endgroup$
– Matti P.
12 hours ago
1
$begingroup$
You are saying that $ye^y=e^{x+1}$ holds for $x=0$ so that $ye^y=e^1=e$? But then, $y=1$ obviously is a solution.
$endgroup$
– James
12 hours ago
3
$begingroup$
"I know $y=1$ but I don't know how to prove it": what about $1e^1=e^{0+1}$ ? :-)
$endgroup$
– Yves Daoust
12 hours ago
3
$begingroup$
There is no real need to introduce $x$ then set it to $0$.
$endgroup$
– Yves Daoust
12 hours ago
$begingroup$
I found it! It's right there at the beginning of your equation!
$endgroup$
– Mason Wheeler
7 hours ago
add a comment |
$begingroup$
The following equation is given: $$ye^y=e^{x+1}$$ when $x=0$. I tried to solve it as logarithmic equation but I can't go further. I know $y=1$ but I don't know how to prove it. Any idea? Thank you😊
exponential-function functional-equations
$endgroup$
The following equation is given: $$ye^y=e^{x+1}$$ when $x=0$. I tried to solve it as logarithmic equation but I can't go further. I know $y=1$ but I don't know how to prove it. Any idea? Thank you😊
exponential-function functional-equations
exponential-function functional-equations
edited 12 hours ago
SNEHIL SANYAL
570110
570110
asked 12 hours ago
AnnaAnna
2617
2617
$begingroup$
Indeed, someone has thought if this problem before: en.wikipedia.org/wiki/Lambert_W_function
$endgroup$
– Matti P.
12 hours ago
1
$begingroup$
You are saying that $ye^y=e^{x+1}$ holds for $x=0$ so that $ye^y=e^1=e$? But then, $y=1$ obviously is a solution.
$endgroup$
– James
12 hours ago
3
$begingroup$
"I know $y=1$ but I don't know how to prove it": what about $1e^1=e^{0+1}$ ? :-)
$endgroup$
– Yves Daoust
12 hours ago
3
$begingroup$
There is no real need to introduce $x$ then set it to $0$.
$endgroup$
– Yves Daoust
12 hours ago
$begingroup$
I found it! It's right there at the beginning of your equation!
$endgroup$
– Mason Wheeler
7 hours ago
add a comment |
$begingroup$
Indeed, someone has thought if this problem before: en.wikipedia.org/wiki/Lambert_W_function
$endgroup$
– Matti P.
12 hours ago
1
$begingroup$
You are saying that $ye^y=e^{x+1}$ holds for $x=0$ so that $ye^y=e^1=e$? But then, $y=1$ obviously is a solution.
$endgroup$
– James
12 hours ago
3
$begingroup$
"I know $y=1$ but I don't know how to prove it": what about $1e^1=e^{0+1}$ ? :-)
$endgroup$
– Yves Daoust
12 hours ago
3
$begingroup$
There is no real need to introduce $x$ then set it to $0$.
$endgroup$
– Yves Daoust
12 hours ago
$begingroup$
I found it! It's right there at the beginning of your equation!
$endgroup$
– Mason Wheeler
7 hours ago
$begingroup$
Indeed, someone has thought if this problem before: en.wikipedia.org/wiki/Lambert_W_function
$endgroup$
– Matti P.
12 hours ago
$begingroup$
Indeed, someone has thought if this problem before: en.wikipedia.org/wiki/Lambert_W_function
$endgroup$
– Matti P.
12 hours ago
1
1
$begingroup$
You are saying that $ye^y=e^{x+1}$ holds for $x=0$ so that $ye^y=e^1=e$? But then, $y=1$ obviously is a solution.
$endgroup$
– James
12 hours ago
$begingroup$
You are saying that $ye^y=e^{x+1}$ holds for $x=0$ so that $ye^y=e^1=e$? But then, $y=1$ obviously is a solution.
$endgroup$
– James
12 hours ago
3
3
$begingroup$
"I know $y=1$ but I don't know how to prove it": what about $1e^1=e^{0+1}$ ? :-)
$endgroup$
– Yves Daoust
12 hours ago
$begingroup$
"I know $y=1$ but I don't know how to prove it": what about $1e^1=e^{0+1}$ ? :-)
$endgroup$
– Yves Daoust
12 hours ago
3
3
$begingroup$
There is no real need to introduce $x$ then set it to $0$.
$endgroup$
– Yves Daoust
12 hours ago
$begingroup$
There is no real need to introduce $x$ then set it to $0$.
$endgroup$
– Yves Daoust
12 hours ago
$begingroup$
I found it! It's right there at the beginning of your equation!
$endgroup$
– Mason Wheeler
7 hours ago
$begingroup$
I found it! It's right there at the beginning of your equation!
$endgroup$
– Mason Wheeler
7 hours ago
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
You may write
- $ye^y = e^{ln y + y} = e^{x+1} Rightarrow ln y + y = 1+x stackrel{x= 0}{Rightarrow} Rightarrow ln y + y = 1 Rightarrow y =1$
The uniqueness of the solution follows from the monotonicity of $ln y+ y$.
$endgroup$
$begingroup$
Can't you just say that $ye^y$ is monotonic ?
$endgroup$
– Yves Daoust
6 hours ago
$begingroup$
Yes, of course. But I just said that $ln y + y$ is monotonic. :-) Even if this gives me a downvote as I have just seen :-D. Funny.
$endgroup$
– trancelocation
5 hours ago
$begingroup$
I can't understand the need to take the logarithm...
$endgroup$
– Yves Daoust
5 hours ago
$begingroup$
I thought MSE is a place where the OPs can see different answers to their questions and may decide for themselves what is most helpful for them. The shortest solution is not always the most helpful depending on the knowledge of the OP.
$endgroup$
– trancelocation
5 hours ago
$begingroup$
I mean that I don't see in what way the logarithm simplifies the resolution.
$endgroup$
– Yves Daoust
5 hours ago
add a comment |
$begingroup$
You can solve this equation by taking logarithms both side with respect to the base $e$.
The equation becomes:
$$ln(ye^y)=ln(e^{x+1})$$
$$ln y+ln e^y=ln (e^{x+1})$$
$$ln y +y = x+1$$
You are given the value of $x=0$, put it in the equation to get:
$$ln y +y =1$$
From the equation, if we put $y=1$ it satisfies the equation. You can also plot a graph for the two functions.

Hope this helps...
$endgroup$
2
$begingroup$
"You can solve this equation by taking logarithms both side": this doesn't help.
$endgroup$
– Yves Daoust
12 hours ago
add a comment |
$begingroup$
If $x=0$, then $y=1$ is obviously a solution. But $e^{x+1}=ecdot e^x>e^x$, and $x+1>x$, hence $xe^x$ is an increasing function. Since $y=1$ solves $ye^y=e$, and $e$ is constant, it is unique.
$endgroup$
add a comment |
Your Answer
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
You may write
- $ye^y = e^{ln y + y} = e^{x+1} Rightarrow ln y + y = 1+x stackrel{x= 0}{Rightarrow} Rightarrow ln y + y = 1 Rightarrow y =1$
The uniqueness of the solution follows from the monotonicity of $ln y+ y$.
$endgroup$
$begingroup$
Can't you just say that $ye^y$ is monotonic ?
$endgroup$
– Yves Daoust
6 hours ago
$begingroup$
Yes, of course. But I just said that $ln y + y$ is monotonic. :-) Even if this gives me a downvote as I have just seen :-D. Funny.
$endgroup$
– trancelocation
5 hours ago
$begingroup$
I can't understand the need to take the logarithm...
$endgroup$
– Yves Daoust
5 hours ago
$begingroup$
I thought MSE is a place where the OPs can see different answers to their questions and may decide for themselves what is most helpful for them. The shortest solution is not always the most helpful depending on the knowledge of the OP.
$endgroup$
– trancelocation
5 hours ago
$begingroup$
I mean that I don't see in what way the logarithm simplifies the resolution.
$endgroup$
– Yves Daoust
5 hours ago
add a comment |
$begingroup$
You may write
- $ye^y = e^{ln y + y} = e^{x+1} Rightarrow ln y + y = 1+x stackrel{x= 0}{Rightarrow} Rightarrow ln y + y = 1 Rightarrow y =1$
The uniqueness of the solution follows from the monotonicity of $ln y+ y$.
$endgroup$
$begingroup$
Can't you just say that $ye^y$ is monotonic ?
$endgroup$
– Yves Daoust
6 hours ago
$begingroup$
Yes, of course. But I just said that $ln y + y$ is monotonic. :-) Even if this gives me a downvote as I have just seen :-D. Funny.
$endgroup$
– trancelocation
5 hours ago
$begingroup$
I can't understand the need to take the logarithm...
$endgroup$
– Yves Daoust
5 hours ago
$begingroup$
I thought MSE is a place where the OPs can see different answers to their questions and may decide for themselves what is most helpful for them. The shortest solution is not always the most helpful depending on the knowledge of the OP.
$endgroup$
– trancelocation
5 hours ago
$begingroup$
I mean that I don't see in what way the logarithm simplifies the resolution.
$endgroup$
– Yves Daoust
5 hours ago
add a comment |
$begingroup$
You may write
- $ye^y = e^{ln y + y} = e^{x+1} Rightarrow ln y + y = 1+x stackrel{x= 0}{Rightarrow} Rightarrow ln y + y = 1 Rightarrow y =1$
The uniqueness of the solution follows from the monotonicity of $ln y+ y$.
$endgroup$
You may write
- $ye^y = e^{ln y + y} = e^{x+1} Rightarrow ln y + y = 1+x stackrel{x= 0}{Rightarrow} Rightarrow ln y + y = 1 Rightarrow y =1$
The uniqueness of the solution follows from the monotonicity of $ln y+ y$.
answered 12 hours ago
trancelocationtrancelocation
12.5k1826
12.5k1826
$begingroup$
Can't you just say that $ye^y$ is monotonic ?
$endgroup$
– Yves Daoust
6 hours ago
$begingroup$
Yes, of course. But I just said that $ln y + y$ is monotonic. :-) Even if this gives me a downvote as I have just seen :-D. Funny.
$endgroup$
– trancelocation
5 hours ago
$begingroup$
I can't understand the need to take the logarithm...
$endgroup$
– Yves Daoust
5 hours ago
$begingroup$
I thought MSE is a place where the OPs can see different answers to their questions and may decide for themselves what is most helpful for them. The shortest solution is not always the most helpful depending on the knowledge of the OP.
$endgroup$
– trancelocation
5 hours ago
$begingroup$
I mean that I don't see in what way the logarithm simplifies the resolution.
$endgroup$
– Yves Daoust
5 hours ago
add a comment |
$begingroup$
Can't you just say that $ye^y$ is monotonic ?
$endgroup$
– Yves Daoust
6 hours ago
$begingroup$
Yes, of course. But I just said that $ln y + y$ is monotonic. :-) Even if this gives me a downvote as I have just seen :-D. Funny.
$endgroup$
– trancelocation
5 hours ago
$begingroup$
I can't understand the need to take the logarithm...
$endgroup$
– Yves Daoust
5 hours ago
$begingroup$
I thought MSE is a place where the OPs can see different answers to their questions and may decide for themselves what is most helpful for them. The shortest solution is not always the most helpful depending on the knowledge of the OP.
$endgroup$
– trancelocation
5 hours ago
$begingroup$
I mean that I don't see in what way the logarithm simplifies the resolution.
$endgroup$
– Yves Daoust
5 hours ago
$begingroup$
Can't you just say that $ye^y$ is monotonic ?
$endgroup$
– Yves Daoust
6 hours ago
$begingroup$
Can't you just say that $ye^y$ is monotonic ?
$endgroup$
– Yves Daoust
6 hours ago
$begingroup$
Yes, of course. But I just said that $ln y + y$ is monotonic. :-) Even if this gives me a downvote as I have just seen :-D. Funny.
$endgroup$
– trancelocation
5 hours ago
$begingroup$
Yes, of course. But I just said that $ln y + y$ is monotonic. :-) Even if this gives me a downvote as I have just seen :-D. Funny.
$endgroup$
– trancelocation
5 hours ago
$begingroup$
I can't understand the need to take the logarithm...
$endgroup$
– Yves Daoust
5 hours ago
$begingroup$
I can't understand the need to take the logarithm...
$endgroup$
– Yves Daoust
5 hours ago
$begingroup$
I thought MSE is a place where the OPs can see different answers to their questions and may decide for themselves what is most helpful for them. The shortest solution is not always the most helpful depending on the knowledge of the OP.
$endgroup$
– trancelocation
5 hours ago
$begingroup$
I thought MSE is a place where the OPs can see different answers to their questions and may decide for themselves what is most helpful for them. The shortest solution is not always the most helpful depending on the knowledge of the OP.
$endgroup$
– trancelocation
5 hours ago
$begingroup$
I mean that I don't see in what way the logarithm simplifies the resolution.
$endgroup$
– Yves Daoust
5 hours ago
$begingroup$
I mean that I don't see in what way the logarithm simplifies the resolution.
$endgroup$
– Yves Daoust
5 hours ago
add a comment |
$begingroup$
You can solve this equation by taking logarithms both side with respect to the base $e$.
The equation becomes:
$$ln(ye^y)=ln(e^{x+1})$$
$$ln y+ln e^y=ln (e^{x+1})$$
$$ln y +y = x+1$$
You are given the value of $x=0$, put it in the equation to get:
$$ln y +y =1$$
From the equation, if we put $y=1$ it satisfies the equation. You can also plot a graph for the two functions.

Hope this helps...
$endgroup$
2
$begingroup$
"You can solve this equation by taking logarithms both side": this doesn't help.
$endgroup$
– Yves Daoust
12 hours ago
add a comment |
$begingroup$
You can solve this equation by taking logarithms both side with respect to the base $e$.
The equation becomes:
$$ln(ye^y)=ln(e^{x+1})$$
$$ln y+ln e^y=ln (e^{x+1})$$
$$ln y +y = x+1$$
You are given the value of $x=0$, put it in the equation to get:
$$ln y +y =1$$
From the equation, if we put $y=1$ it satisfies the equation. You can also plot a graph for the two functions.

Hope this helps...
$endgroup$
2
$begingroup$
"You can solve this equation by taking logarithms both side": this doesn't help.
$endgroup$
– Yves Daoust
12 hours ago
add a comment |
$begingroup$
You can solve this equation by taking logarithms both side with respect to the base $e$.
The equation becomes:
$$ln(ye^y)=ln(e^{x+1})$$
$$ln y+ln e^y=ln (e^{x+1})$$
$$ln y +y = x+1$$
You are given the value of $x=0$, put it in the equation to get:
$$ln y +y =1$$
From the equation, if we put $y=1$ it satisfies the equation. You can also plot a graph for the two functions.

Hope this helps...
$endgroup$
You can solve this equation by taking logarithms both side with respect to the base $e$.
The equation becomes:
$$ln(ye^y)=ln(e^{x+1})$$
$$ln y+ln e^y=ln (e^{x+1})$$
$$ln y +y = x+1$$
You are given the value of $x=0$, put it in the equation to get:
$$ln y +y =1$$
From the equation, if we put $y=1$ it satisfies the equation. You can also plot a graph for the two functions.

Hope this helps...
answered 12 hours ago
SNEHIL SANYALSNEHIL SANYAL
570110
570110
2
$begingroup$
"You can solve this equation by taking logarithms both side": this doesn't help.
$endgroup$
– Yves Daoust
12 hours ago
add a comment |
2
$begingroup$
"You can solve this equation by taking logarithms both side": this doesn't help.
$endgroup$
– Yves Daoust
12 hours ago
2
2
$begingroup$
"You can solve this equation by taking logarithms both side": this doesn't help.
$endgroup$
– Yves Daoust
12 hours ago
$begingroup$
"You can solve this equation by taking logarithms both side": this doesn't help.
$endgroup$
– Yves Daoust
12 hours ago
add a comment |
$begingroup$
If $x=0$, then $y=1$ is obviously a solution. But $e^{x+1}=ecdot e^x>e^x$, and $x+1>x$, hence $xe^x$ is an increasing function. Since $y=1$ solves $ye^y=e$, and $e$ is constant, it is unique.
$endgroup$
add a comment |
$begingroup$
If $x=0$, then $y=1$ is obviously a solution. But $e^{x+1}=ecdot e^x>e^x$, and $x+1>x$, hence $xe^x$ is an increasing function. Since $y=1$ solves $ye^y=e$, and $e$ is constant, it is unique.
$endgroup$
add a comment |
$begingroup$
If $x=0$, then $y=1$ is obviously a solution. But $e^{x+1}=ecdot e^x>e^x$, and $x+1>x$, hence $xe^x$ is an increasing function. Since $y=1$ solves $ye^y=e$, and $e$ is constant, it is unique.
$endgroup$
If $x=0$, then $y=1$ is obviously a solution. But $e^{x+1}=ecdot e^x>e^x$, and $x+1>x$, hence $xe^x$ is an increasing function. Since $y=1$ solves $ye^y=e$, and $e$ is constant, it is unique.
answered 12 hours ago
YiFanYiFan
4,3241627
4,3241627
add a comment |
add a comment |
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$begingroup$
Indeed, someone has thought if this problem before: en.wikipedia.org/wiki/Lambert_W_function
$endgroup$
– Matti P.
12 hours ago
1
$begingroup$
You are saying that $ye^y=e^{x+1}$ holds for $x=0$ so that $ye^y=e^1=e$? But then, $y=1$ obviously is a solution.
$endgroup$
– James
12 hours ago
3
$begingroup$
"I know $y=1$ but I don't know how to prove it": what about $1e^1=e^{0+1}$ ? :-)
$endgroup$
– Yves Daoust
12 hours ago
3
$begingroup$
There is no real need to introduce $x$ then set it to $0$.
$endgroup$
– Yves Daoust
12 hours ago
$begingroup$
I found it! It's right there at the beginning of your equation!
$endgroup$
– Mason Wheeler
7 hours ago