Can we solve a simple set of equations in radicals?












2












$begingroup$


Suppose $x,y,z$ are non-zero coprime integers with $x+y ne z$ and which satisfy the following three equations:




  • $operatorname{rad}(x)=operatorname{rad}(z-y)$

  • $operatorname{rad}(y)=operatorname{rad}(z-x)$

  • $operatorname{rad}(z)=operatorname{rad}(x+y)$


Here, the radical of $n$ is defined as the product of all prime divisors of $n$. Hence $operatorname{rad}(n)=prod_{p|n}{p}$.



It is not difficult to check that if $(x,y,z)$ is a solution, also $(-x,-y,-z)$ and $(y,x,z),(z,-x,y),(-y,z,x)$ are solutions. Beside these symmetries, can we prove that $(5,27,2)$ is the only coprime solution?










share|cite|improve this question











$endgroup$












  • $begingroup$
    Have you checked this for a number of values?
    $endgroup$
    – marty cohen
    Nov 1 '15 at 22:34










  • $begingroup$
    Are these pairwise coprime, or is gcd(x, y, z) = 1?
    $endgroup$
    – marty cohen
    Nov 1 '15 at 22:36










  • $begingroup$
    I checked it for the range $x,y,z in [1, dots ,500]$.
    $endgroup$
    – Rolandb
    Nov 2 '15 at 6:10










  • $begingroup$
    I meant $gcd(x,y,z)=1$ but numerically for this range, pairwise coprime yields the same result. @marty
    $endgroup$
    – Rolandb
    Nov 2 '15 at 6:19
















2












$begingroup$


Suppose $x,y,z$ are non-zero coprime integers with $x+y ne z$ and which satisfy the following three equations:




  • $operatorname{rad}(x)=operatorname{rad}(z-y)$

  • $operatorname{rad}(y)=operatorname{rad}(z-x)$

  • $operatorname{rad}(z)=operatorname{rad}(x+y)$


Here, the radical of $n$ is defined as the product of all prime divisors of $n$. Hence $operatorname{rad}(n)=prod_{p|n}{p}$.



It is not difficult to check that if $(x,y,z)$ is a solution, also $(-x,-y,-z)$ and $(y,x,z),(z,-x,y),(-y,z,x)$ are solutions. Beside these symmetries, can we prove that $(5,27,2)$ is the only coprime solution?










share|cite|improve this question











$endgroup$












  • $begingroup$
    Have you checked this for a number of values?
    $endgroup$
    – marty cohen
    Nov 1 '15 at 22:34










  • $begingroup$
    Are these pairwise coprime, or is gcd(x, y, z) = 1?
    $endgroup$
    – marty cohen
    Nov 1 '15 at 22:36










  • $begingroup$
    I checked it for the range $x,y,z in [1, dots ,500]$.
    $endgroup$
    – Rolandb
    Nov 2 '15 at 6:10










  • $begingroup$
    I meant $gcd(x,y,z)=1$ but numerically for this range, pairwise coprime yields the same result. @marty
    $endgroup$
    – Rolandb
    Nov 2 '15 at 6:19














2












2








2





$begingroup$


Suppose $x,y,z$ are non-zero coprime integers with $x+y ne z$ and which satisfy the following three equations:




  • $operatorname{rad}(x)=operatorname{rad}(z-y)$

  • $operatorname{rad}(y)=operatorname{rad}(z-x)$

  • $operatorname{rad}(z)=operatorname{rad}(x+y)$


Here, the radical of $n$ is defined as the product of all prime divisors of $n$. Hence $operatorname{rad}(n)=prod_{p|n}{p}$.



It is not difficult to check that if $(x,y,z)$ is a solution, also $(-x,-y,-z)$ and $(y,x,z),(z,-x,y),(-y,z,x)$ are solutions. Beside these symmetries, can we prove that $(5,27,2)$ is the only coprime solution?










share|cite|improve this question











$endgroup$




Suppose $x,y,z$ are non-zero coprime integers with $x+y ne z$ and which satisfy the following three equations:




  • $operatorname{rad}(x)=operatorname{rad}(z-y)$

  • $operatorname{rad}(y)=operatorname{rad}(z-x)$

  • $operatorname{rad}(z)=operatorname{rad}(x+y)$


Here, the radical of $n$ is defined as the product of all prime divisors of $n$. Hence $operatorname{rad}(n)=prod_{p|n}{p}$.



It is not difficult to check that if $(x,y,z)$ is a solution, also $(-x,-y,-z)$ and $(y,x,z),(z,-x,y),(-y,z,x)$ are solutions. Beside these symmetries, can we prove that $(5,27,2)$ is the only coprime solution?







number-theory






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Dec 22 '18 at 20:43







Rolandb

















asked Nov 1 '15 at 20:56









RolandbRolandb

1226




1226












  • $begingroup$
    Have you checked this for a number of values?
    $endgroup$
    – marty cohen
    Nov 1 '15 at 22:34










  • $begingroup$
    Are these pairwise coprime, or is gcd(x, y, z) = 1?
    $endgroup$
    – marty cohen
    Nov 1 '15 at 22:36










  • $begingroup$
    I checked it for the range $x,y,z in [1, dots ,500]$.
    $endgroup$
    – Rolandb
    Nov 2 '15 at 6:10










  • $begingroup$
    I meant $gcd(x,y,z)=1$ but numerically for this range, pairwise coprime yields the same result. @marty
    $endgroup$
    – Rolandb
    Nov 2 '15 at 6:19


















  • $begingroup$
    Have you checked this for a number of values?
    $endgroup$
    – marty cohen
    Nov 1 '15 at 22:34










  • $begingroup$
    Are these pairwise coprime, or is gcd(x, y, z) = 1?
    $endgroup$
    – marty cohen
    Nov 1 '15 at 22:36










  • $begingroup$
    I checked it for the range $x,y,z in [1, dots ,500]$.
    $endgroup$
    – Rolandb
    Nov 2 '15 at 6:10










  • $begingroup$
    I meant $gcd(x,y,z)=1$ but numerically for this range, pairwise coprime yields the same result. @marty
    $endgroup$
    – Rolandb
    Nov 2 '15 at 6:19
















$begingroup$
Have you checked this for a number of values?
$endgroup$
– marty cohen
Nov 1 '15 at 22:34




$begingroup$
Have you checked this for a number of values?
$endgroup$
– marty cohen
Nov 1 '15 at 22:34












$begingroup$
Are these pairwise coprime, or is gcd(x, y, z) = 1?
$endgroup$
– marty cohen
Nov 1 '15 at 22:36




$begingroup$
Are these pairwise coprime, or is gcd(x, y, z) = 1?
$endgroup$
– marty cohen
Nov 1 '15 at 22:36












$begingroup$
I checked it for the range $x,y,z in [1, dots ,500]$.
$endgroup$
– Rolandb
Nov 2 '15 at 6:10




$begingroup$
I checked it for the range $x,y,z in [1, dots ,500]$.
$endgroup$
– Rolandb
Nov 2 '15 at 6:10












$begingroup$
I meant $gcd(x,y,z)=1$ but numerically for this range, pairwise coprime yields the same result. @marty
$endgroup$
– Rolandb
Nov 2 '15 at 6:19




$begingroup$
I meant $gcd(x,y,z)=1$ but numerically for this range, pairwise coprime yields the same result. @marty
$endgroup$
– Rolandb
Nov 2 '15 at 6:19










1 Answer
1






active

oldest

votes


















-1












$begingroup$

I found a general expression for a solution. For some power $m$ we have an integer $s$ such that $text{rad}(x)^m=sx$. For instance $x=-2^3.3$ we have $text{rad}(x)=2.3$ and $s=-3^2$.
In general $m=n$ works.



Using this observation, there are pairs of non-zero integers $(a,b),(c,d),(e,f)$ such that
$$begin{matrix}
a x=b (z-y)\
c y=d (z-x)\
e z=f (x+y)\
end{matrix}$$

Note that we can assume that the pairs $(a,b),(c,d),(e,f)$ are coprime as we can remove the common factor.



We can solve this set of equations and find
$$x=z.dfrac{b(c-d)}{ac-bd} text{ and } y = z.dfrac{d(a-b)}{ac-bd}$$
We have $ac-bd ne 0$ as $ac=bd$ implies that $xy=(z-y)(z-x)=z(z-x-y)+xy$ and hence $z(z-x-y)=0$ which is not possible.



Clearly, if $x$ and $z$ are coprime we must have that $z mid ac-bd$. How can we prove that $(5,27,2)$ is the only coprime solution (up to symmetry)?






share|cite|improve this answer











$endgroup$













  • $begingroup$
    It's not clear to me what values you mean to give to $x$, $y$, and $z$.
    $endgroup$
    – Gerry Myerson
    Nov 3 '15 at 6:29










  • $begingroup$
    $x=2^{13}$, $y=5^2.7^3$, $z=3^6.23$ and $x=2^7$, $y=5^6.7$, $z=3^2.23^3$.
    $endgroup$
    – Rolandb
    Nov 3 '15 at 19:08










  • $begingroup$
    But the question didn't ask for two sets $x,y,z$ with the same radical of $xyz$. I don't see how what you have written relates to the question at all.
    $endgroup$
    – Gerry Myerson
    Nov 3 '15 at 22:23










  • $begingroup$
    Are you still there?
    $endgroup$
    – Gerry Myerson
    Nov 5 '15 at 4:53










  • $begingroup$
    Apologies. I made a mistake but I could not respond earlier. A proof is added.
    $endgroup$
    – Rolandb
    Nov 8 '15 at 12:22











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1 Answer
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active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









-1












$begingroup$

I found a general expression for a solution. For some power $m$ we have an integer $s$ such that $text{rad}(x)^m=sx$. For instance $x=-2^3.3$ we have $text{rad}(x)=2.3$ and $s=-3^2$.
In general $m=n$ works.



Using this observation, there are pairs of non-zero integers $(a,b),(c,d),(e,f)$ such that
$$begin{matrix}
a x=b (z-y)\
c y=d (z-x)\
e z=f (x+y)\
end{matrix}$$

Note that we can assume that the pairs $(a,b),(c,d),(e,f)$ are coprime as we can remove the common factor.



We can solve this set of equations and find
$$x=z.dfrac{b(c-d)}{ac-bd} text{ and } y = z.dfrac{d(a-b)}{ac-bd}$$
We have $ac-bd ne 0$ as $ac=bd$ implies that $xy=(z-y)(z-x)=z(z-x-y)+xy$ and hence $z(z-x-y)=0$ which is not possible.



Clearly, if $x$ and $z$ are coprime we must have that $z mid ac-bd$. How can we prove that $(5,27,2)$ is the only coprime solution (up to symmetry)?






share|cite|improve this answer











$endgroup$













  • $begingroup$
    It's not clear to me what values you mean to give to $x$, $y$, and $z$.
    $endgroup$
    – Gerry Myerson
    Nov 3 '15 at 6:29










  • $begingroup$
    $x=2^{13}$, $y=5^2.7^3$, $z=3^6.23$ and $x=2^7$, $y=5^6.7$, $z=3^2.23^3$.
    $endgroup$
    – Rolandb
    Nov 3 '15 at 19:08










  • $begingroup$
    But the question didn't ask for two sets $x,y,z$ with the same radical of $xyz$. I don't see how what you have written relates to the question at all.
    $endgroup$
    – Gerry Myerson
    Nov 3 '15 at 22:23










  • $begingroup$
    Are you still there?
    $endgroup$
    – Gerry Myerson
    Nov 5 '15 at 4:53










  • $begingroup$
    Apologies. I made a mistake but I could not respond earlier. A proof is added.
    $endgroup$
    – Rolandb
    Nov 8 '15 at 12:22
















-1












$begingroup$

I found a general expression for a solution. For some power $m$ we have an integer $s$ such that $text{rad}(x)^m=sx$. For instance $x=-2^3.3$ we have $text{rad}(x)=2.3$ and $s=-3^2$.
In general $m=n$ works.



Using this observation, there are pairs of non-zero integers $(a,b),(c,d),(e,f)$ such that
$$begin{matrix}
a x=b (z-y)\
c y=d (z-x)\
e z=f (x+y)\
end{matrix}$$

Note that we can assume that the pairs $(a,b),(c,d),(e,f)$ are coprime as we can remove the common factor.



We can solve this set of equations and find
$$x=z.dfrac{b(c-d)}{ac-bd} text{ and } y = z.dfrac{d(a-b)}{ac-bd}$$
We have $ac-bd ne 0$ as $ac=bd$ implies that $xy=(z-y)(z-x)=z(z-x-y)+xy$ and hence $z(z-x-y)=0$ which is not possible.



Clearly, if $x$ and $z$ are coprime we must have that $z mid ac-bd$. How can we prove that $(5,27,2)$ is the only coprime solution (up to symmetry)?






share|cite|improve this answer











$endgroup$













  • $begingroup$
    It's not clear to me what values you mean to give to $x$, $y$, and $z$.
    $endgroup$
    – Gerry Myerson
    Nov 3 '15 at 6:29










  • $begingroup$
    $x=2^{13}$, $y=5^2.7^3$, $z=3^6.23$ and $x=2^7$, $y=5^6.7$, $z=3^2.23^3$.
    $endgroup$
    – Rolandb
    Nov 3 '15 at 19:08










  • $begingroup$
    But the question didn't ask for two sets $x,y,z$ with the same radical of $xyz$. I don't see how what you have written relates to the question at all.
    $endgroup$
    – Gerry Myerson
    Nov 3 '15 at 22:23










  • $begingroup$
    Are you still there?
    $endgroup$
    – Gerry Myerson
    Nov 5 '15 at 4:53










  • $begingroup$
    Apologies. I made a mistake but I could not respond earlier. A proof is added.
    $endgroup$
    – Rolandb
    Nov 8 '15 at 12:22














-1












-1








-1





$begingroup$

I found a general expression for a solution. For some power $m$ we have an integer $s$ such that $text{rad}(x)^m=sx$. For instance $x=-2^3.3$ we have $text{rad}(x)=2.3$ and $s=-3^2$.
In general $m=n$ works.



Using this observation, there are pairs of non-zero integers $(a,b),(c,d),(e,f)$ such that
$$begin{matrix}
a x=b (z-y)\
c y=d (z-x)\
e z=f (x+y)\
end{matrix}$$

Note that we can assume that the pairs $(a,b),(c,d),(e,f)$ are coprime as we can remove the common factor.



We can solve this set of equations and find
$$x=z.dfrac{b(c-d)}{ac-bd} text{ and } y = z.dfrac{d(a-b)}{ac-bd}$$
We have $ac-bd ne 0$ as $ac=bd$ implies that $xy=(z-y)(z-x)=z(z-x-y)+xy$ and hence $z(z-x-y)=0$ which is not possible.



Clearly, if $x$ and $z$ are coprime we must have that $z mid ac-bd$. How can we prove that $(5,27,2)$ is the only coprime solution (up to symmetry)?






share|cite|improve this answer











$endgroup$



I found a general expression for a solution. For some power $m$ we have an integer $s$ such that $text{rad}(x)^m=sx$. For instance $x=-2^3.3$ we have $text{rad}(x)=2.3$ and $s=-3^2$.
In general $m=n$ works.



Using this observation, there are pairs of non-zero integers $(a,b),(c,d),(e,f)$ such that
$$begin{matrix}
a x=b (z-y)\
c y=d (z-x)\
e z=f (x+y)\
end{matrix}$$

Note that we can assume that the pairs $(a,b),(c,d),(e,f)$ are coprime as we can remove the common factor.



We can solve this set of equations and find
$$x=z.dfrac{b(c-d)}{ac-bd} text{ and } y = z.dfrac{d(a-b)}{ac-bd}$$
We have $ac-bd ne 0$ as $ac=bd$ implies that $xy=(z-y)(z-x)=z(z-x-y)+xy$ and hence $z(z-x-y)=0$ which is not possible.



Clearly, if $x$ and $z$ are coprime we must have that $z mid ac-bd$. How can we prove that $(5,27,2)$ is the only coprime solution (up to symmetry)?







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited Dec 22 '18 at 20:42

























answered Nov 3 '15 at 5:45









RolandbRolandb

1226




1226












  • $begingroup$
    It's not clear to me what values you mean to give to $x$, $y$, and $z$.
    $endgroup$
    – Gerry Myerson
    Nov 3 '15 at 6:29










  • $begingroup$
    $x=2^{13}$, $y=5^2.7^3$, $z=3^6.23$ and $x=2^7$, $y=5^6.7$, $z=3^2.23^3$.
    $endgroup$
    – Rolandb
    Nov 3 '15 at 19:08










  • $begingroup$
    But the question didn't ask for two sets $x,y,z$ with the same radical of $xyz$. I don't see how what you have written relates to the question at all.
    $endgroup$
    – Gerry Myerson
    Nov 3 '15 at 22:23










  • $begingroup$
    Are you still there?
    $endgroup$
    – Gerry Myerson
    Nov 5 '15 at 4:53










  • $begingroup$
    Apologies. I made a mistake but I could not respond earlier. A proof is added.
    $endgroup$
    – Rolandb
    Nov 8 '15 at 12:22


















  • $begingroup$
    It's not clear to me what values you mean to give to $x$, $y$, and $z$.
    $endgroup$
    – Gerry Myerson
    Nov 3 '15 at 6:29










  • $begingroup$
    $x=2^{13}$, $y=5^2.7^3$, $z=3^6.23$ and $x=2^7$, $y=5^6.7$, $z=3^2.23^3$.
    $endgroup$
    – Rolandb
    Nov 3 '15 at 19:08










  • $begingroup$
    But the question didn't ask for two sets $x,y,z$ with the same radical of $xyz$. I don't see how what you have written relates to the question at all.
    $endgroup$
    – Gerry Myerson
    Nov 3 '15 at 22:23










  • $begingroup$
    Are you still there?
    $endgroup$
    – Gerry Myerson
    Nov 5 '15 at 4:53










  • $begingroup$
    Apologies. I made a mistake but I could not respond earlier. A proof is added.
    $endgroup$
    – Rolandb
    Nov 8 '15 at 12:22
















$begingroup$
It's not clear to me what values you mean to give to $x$, $y$, and $z$.
$endgroup$
– Gerry Myerson
Nov 3 '15 at 6:29




$begingroup$
It's not clear to me what values you mean to give to $x$, $y$, and $z$.
$endgroup$
– Gerry Myerson
Nov 3 '15 at 6:29












$begingroup$
$x=2^{13}$, $y=5^2.7^3$, $z=3^6.23$ and $x=2^7$, $y=5^6.7$, $z=3^2.23^3$.
$endgroup$
– Rolandb
Nov 3 '15 at 19:08




$begingroup$
$x=2^{13}$, $y=5^2.7^3$, $z=3^6.23$ and $x=2^7$, $y=5^6.7$, $z=3^2.23^3$.
$endgroup$
– Rolandb
Nov 3 '15 at 19:08












$begingroup$
But the question didn't ask for two sets $x,y,z$ with the same radical of $xyz$. I don't see how what you have written relates to the question at all.
$endgroup$
– Gerry Myerson
Nov 3 '15 at 22:23




$begingroup$
But the question didn't ask for two sets $x,y,z$ with the same radical of $xyz$. I don't see how what you have written relates to the question at all.
$endgroup$
– Gerry Myerson
Nov 3 '15 at 22:23












$begingroup$
Are you still there?
$endgroup$
– Gerry Myerson
Nov 5 '15 at 4:53




$begingroup$
Are you still there?
$endgroup$
– Gerry Myerson
Nov 5 '15 at 4:53












$begingroup$
Apologies. I made a mistake but I could not respond earlier. A proof is added.
$endgroup$
– Rolandb
Nov 8 '15 at 12:22




$begingroup$
Apologies. I made a mistake but I could not respond earlier. A proof is added.
$endgroup$
– Rolandb
Nov 8 '15 at 12:22


















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