$(m,n)=1$, what could $(3n-4m, 5n+m)$ be?
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This is what I have so far:
let's say $d$ is the common divisor of $3n-4m$ and $5n+m$, then $d$ divides $5(3n-4m)-3(5n+m)=-23m$ and $3n-4m+4(5n+m)=23n$. $d$ can't be a divisor of both $m$ and $n$, so 23 must divide $d$. But is this the greatest common divisor of $3n-4m$ and $5n+m$?
number-theory
$endgroup$
add a comment |
$begingroup$
This is what I have so far:
let's say $d$ is the common divisor of $3n-4m$ and $5n+m$, then $d$ divides $5(3n-4m)-3(5n+m)=-23m$ and $3n-4m+4(5n+m)=23n$. $d$ can't be a divisor of both $m$ and $n$, so 23 must divide $d$. But is this the greatest common divisor of $3n-4m$ and $5n+m$?
number-theory
$endgroup$
$begingroup$
In my understanding your conclusion does not look correct, because $d$ can divide both $m$ and $n$, and in that case it is equal to $1$. Otherwise, it divides $23$, hence it is either $1$ or $23$.
$endgroup$
– Gibbs
Dec 6 '18 at 23:41
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What does $(m/n)$ mean???
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– bof
Dec 6 '18 at 23:42
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I meant the greatest common divisor.
$endgroup$
– Lowkey
Dec 6 '18 at 23:45
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Um don't you mean $d$ must divide $23$. Not $23$ must divide $d$?
$endgroup$
– fleablood
Dec 7 '18 at 1:33
add a comment |
$begingroup$
This is what I have so far:
let's say $d$ is the common divisor of $3n-4m$ and $5n+m$, then $d$ divides $5(3n-4m)-3(5n+m)=-23m$ and $3n-4m+4(5n+m)=23n$. $d$ can't be a divisor of both $m$ and $n$, so 23 must divide $d$. But is this the greatest common divisor of $3n-4m$ and $5n+m$?
number-theory
$endgroup$
This is what I have so far:
let's say $d$ is the common divisor of $3n-4m$ and $5n+m$, then $d$ divides $5(3n-4m)-3(5n+m)=-23m$ and $3n-4m+4(5n+m)=23n$. $d$ can't be a divisor of both $m$ and $n$, so 23 must divide $d$. But is this the greatest common divisor of $3n-4m$ and $5n+m$?
number-theory
number-theory
edited Dec 6 '18 at 23:43
Lowkey
asked Dec 6 '18 at 23:25
LowkeyLowkey
728
728
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In my understanding your conclusion does not look correct, because $d$ can divide both $m$ and $n$, and in that case it is equal to $1$. Otherwise, it divides $23$, hence it is either $1$ or $23$.
$endgroup$
– Gibbs
Dec 6 '18 at 23:41
$begingroup$
What does $(m/n)$ mean???
$endgroup$
– bof
Dec 6 '18 at 23:42
$begingroup$
I meant the greatest common divisor.
$endgroup$
– Lowkey
Dec 6 '18 at 23:45
$begingroup$
Um don't you mean $d$ must divide $23$. Not $23$ must divide $d$?
$endgroup$
– fleablood
Dec 7 '18 at 1:33
add a comment |
$begingroup$
In my understanding your conclusion does not look correct, because $d$ can divide both $m$ and $n$, and in that case it is equal to $1$. Otherwise, it divides $23$, hence it is either $1$ or $23$.
$endgroup$
– Gibbs
Dec 6 '18 at 23:41
$begingroup$
What does $(m/n)$ mean???
$endgroup$
– bof
Dec 6 '18 at 23:42
$begingroup$
I meant the greatest common divisor.
$endgroup$
– Lowkey
Dec 6 '18 at 23:45
$begingroup$
Um don't you mean $d$ must divide $23$. Not $23$ must divide $d$?
$endgroup$
– fleablood
Dec 7 '18 at 1:33
$begingroup$
In my understanding your conclusion does not look correct, because $d$ can divide both $m$ and $n$, and in that case it is equal to $1$. Otherwise, it divides $23$, hence it is either $1$ or $23$.
$endgroup$
– Gibbs
Dec 6 '18 at 23:41
$begingroup$
In my understanding your conclusion does not look correct, because $d$ can divide both $m$ and $n$, and in that case it is equal to $1$. Otherwise, it divides $23$, hence it is either $1$ or $23$.
$endgroup$
– Gibbs
Dec 6 '18 at 23:41
$begingroup$
What does $(m/n)$ mean???
$endgroup$
– bof
Dec 6 '18 at 23:42
$begingroup$
What does $(m/n)$ mean???
$endgroup$
– bof
Dec 6 '18 at 23:42
$begingroup$
I meant the greatest common divisor.
$endgroup$
– Lowkey
Dec 6 '18 at 23:45
$begingroup$
I meant the greatest common divisor.
$endgroup$
– Lowkey
Dec 6 '18 at 23:45
$begingroup$
Um don't you mean $d$ must divide $23$. Not $23$ must divide $d$?
$endgroup$
– fleablood
Dec 7 '18 at 1:33
$begingroup$
Um don't you mean $d$ must divide $23$. Not $23$ must divide $d$?
$endgroup$
– fleablood
Dec 7 '18 at 1:33
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
You have the right idea - eliminate $n$ and $m,,$ but your conclusion is misworded (reversed). It should state that $23$ must be divisible by $d$ (not $23$ must divide $d$) since $$,dmid 23m,23niff dmid (23m,23n)! =! 23(m,n)! =! 23 {rm by} (m,n)=1$$
Remark $ $ We can use linear algebra language, i.e. use Cramer's rule to solve for $,m,n,$ below
$qquadqquadqquad$ $ begin{eqnarray}
3 n, - 4,m & = & i\[.3em]
5,n +, 1,m &=& j end{eqnarray}quadRightarrowquad
$ $
begin{align}
23,n &= , i +, 4,j \[.3em]
23,m, &=, -5,i + 3,j end{align} $
Thus by RHS: $,dmid i,j,Rightarrow, dmid 23m,23n,Rightarrow, dmid 23 $ as above. More generally this method yields
Theorem $ $ If $rm,[x,y]overset{A}mapsto [X,Y],$ is linear then $: rm(x,y)mid (X,Y)mid color{#90f}Delta, (x,y), color{#90f}{Delta := {rm det}, A}$
e.g. $ $ in OP we have $,color{#90f}{Delta =bf 23},$ so the above yields $ (3n!-!4m,5n!+!m)midcolor{#90f}{bf 23}(n,m) = 23$
using the map $ [n,m]mapsto [3n!-!4m,,5n!+!m] $ i.e.
$$ [n,,m],mapsto, [n,,m],underbrace{begin{bmatrix}3 & 5\ -4 &1end{bmatrix}}_{large det A, =, color{#90f}{bf 23}} =, [3n!-!4m,,5n!+!m]$$
$endgroup$
$begingroup$
Thanks for explaining where I went wrong, and then providing more interesting information!
$endgroup$
– Lowkey
Dec 7 '18 at 1:46
add a comment |
$begingroup$
If $m=3$ and $n=4$, the greatest common divisor of $3n-4m=0$ and $5n+m=23$ is $23$.
If $m=1$ and $n=1$, the greatest common divisor of $3n-4m=-1$ and $5n+m=6$ is $1$.
Your argument is good, but the conclusion is wrong: you prove that $d$ can be a divisor of $23$. Thus it is either $1$ or $23$.
$endgroup$
$begingroup$
Thanks, this clears things up.
$endgroup$
– Lowkey
Dec 6 '18 at 23:49
add a comment |
$begingroup$
By Bezout we have $An+Bm=1$, multiply this by $23$ and create some terms
begin{eqnarray*}
20An+4Am-4Am+3An+20Bm-15Bn+15Bn+3Bm=23.
end{eqnarray*}
Now factorise
begin{eqnarray*}
(4A+3B)(m+5n) +(A-5B)(3n-4m) =23.
end{eqnarray*}
So if $(4A+3B,A-5B)=1$ then $(m+5n,3n-4m)=23$ and
and if $(4A+3B,A-5B)=23$ then $(m+5n,3n-4m)=1$.
$endgroup$
add a comment |
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3 Answers
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3 Answers
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$begingroup$
You have the right idea - eliminate $n$ and $m,,$ but your conclusion is misworded (reversed). It should state that $23$ must be divisible by $d$ (not $23$ must divide $d$) since $$,dmid 23m,23niff dmid (23m,23n)! =! 23(m,n)! =! 23 {rm by} (m,n)=1$$
Remark $ $ We can use linear algebra language, i.e. use Cramer's rule to solve for $,m,n,$ below
$qquadqquadqquad$ $ begin{eqnarray}
3 n, - 4,m & = & i\[.3em]
5,n +, 1,m &=& j end{eqnarray}quadRightarrowquad
$ $
begin{align}
23,n &= , i +, 4,j \[.3em]
23,m, &=, -5,i + 3,j end{align} $
Thus by RHS: $,dmid i,j,Rightarrow, dmid 23m,23n,Rightarrow, dmid 23 $ as above. More generally this method yields
Theorem $ $ If $rm,[x,y]overset{A}mapsto [X,Y],$ is linear then $: rm(x,y)mid (X,Y)mid color{#90f}Delta, (x,y), color{#90f}{Delta := {rm det}, A}$
e.g. $ $ in OP we have $,color{#90f}{Delta =bf 23},$ so the above yields $ (3n!-!4m,5n!+!m)midcolor{#90f}{bf 23}(n,m) = 23$
using the map $ [n,m]mapsto [3n!-!4m,,5n!+!m] $ i.e.
$$ [n,,m],mapsto, [n,,m],underbrace{begin{bmatrix}3 & 5\ -4 &1end{bmatrix}}_{large det A, =, color{#90f}{bf 23}} =, [3n!-!4m,,5n!+!m]$$
$endgroup$
$begingroup$
Thanks for explaining where I went wrong, and then providing more interesting information!
$endgroup$
– Lowkey
Dec 7 '18 at 1:46
add a comment |
$begingroup$
You have the right idea - eliminate $n$ and $m,,$ but your conclusion is misworded (reversed). It should state that $23$ must be divisible by $d$ (not $23$ must divide $d$) since $$,dmid 23m,23niff dmid (23m,23n)! =! 23(m,n)! =! 23 {rm by} (m,n)=1$$
Remark $ $ We can use linear algebra language, i.e. use Cramer's rule to solve for $,m,n,$ below
$qquadqquadqquad$ $ begin{eqnarray}
3 n, - 4,m & = & i\[.3em]
5,n +, 1,m &=& j end{eqnarray}quadRightarrowquad
$ $
begin{align}
23,n &= , i +, 4,j \[.3em]
23,m, &=, -5,i + 3,j end{align} $
Thus by RHS: $,dmid i,j,Rightarrow, dmid 23m,23n,Rightarrow, dmid 23 $ as above. More generally this method yields
Theorem $ $ If $rm,[x,y]overset{A}mapsto [X,Y],$ is linear then $: rm(x,y)mid (X,Y)mid color{#90f}Delta, (x,y), color{#90f}{Delta := {rm det}, A}$
e.g. $ $ in OP we have $,color{#90f}{Delta =bf 23},$ so the above yields $ (3n!-!4m,5n!+!m)midcolor{#90f}{bf 23}(n,m) = 23$
using the map $ [n,m]mapsto [3n!-!4m,,5n!+!m] $ i.e.
$$ [n,,m],mapsto, [n,,m],underbrace{begin{bmatrix}3 & 5\ -4 &1end{bmatrix}}_{large det A, =, color{#90f}{bf 23}} =, [3n!-!4m,,5n!+!m]$$
$endgroup$
$begingroup$
Thanks for explaining where I went wrong, and then providing more interesting information!
$endgroup$
– Lowkey
Dec 7 '18 at 1:46
add a comment |
$begingroup$
You have the right idea - eliminate $n$ and $m,,$ but your conclusion is misworded (reversed). It should state that $23$ must be divisible by $d$ (not $23$ must divide $d$) since $$,dmid 23m,23niff dmid (23m,23n)! =! 23(m,n)! =! 23 {rm by} (m,n)=1$$
Remark $ $ We can use linear algebra language, i.e. use Cramer's rule to solve for $,m,n,$ below
$qquadqquadqquad$ $ begin{eqnarray}
3 n, - 4,m & = & i\[.3em]
5,n +, 1,m &=& j end{eqnarray}quadRightarrowquad
$ $
begin{align}
23,n &= , i +, 4,j \[.3em]
23,m, &=, -5,i + 3,j end{align} $
Thus by RHS: $,dmid i,j,Rightarrow, dmid 23m,23n,Rightarrow, dmid 23 $ as above. More generally this method yields
Theorem $ $ If $rm,[x,y]overset{A}mapsto [X,Y],$ is linear then $: rm(x,y)mid (X,Y)mid color{#90f}Delta, (x,y), color{#90f}{Delta := {rm det}, A}$
e.g. $ $ in OP we have $,color{#90f}{Delta =bf 23},$ so the above yields $ (3n!-!4m,5n!+!m)midcolor{#90f}{bf 23}(n,m) = 23$
using the map $ [n,m]mapsto [3n!-!4m,,5n!+!m] $ i.e.
$$ [n,,m],mapsto, [n,,m],underbrace{begin{bmatrix}3 & 5\ -4 &1end{bmatrix}}_{large det A, =, color{#90f}{bf 23}} =, [3n!-!4m,,5n!+!m]$$
$endgroup$
You have the right idea - eliminate $n$ and $m,,$ but your conclusion is misworded (reversed). It should state that $23$ must be divisible by $d$ (not $23$ must divide $d$) since $$,dmid 23m,23niff dmid (23m,23n)! =! 23(m,n)! =! 23 {rm by} (m,n)=1$$
Remark $ $ We can use linear algebra language, i.e. use Cramer's rule to solve for $,m,n,$ below
$qquadqquadqquad$ $ begin{eqnarray}
3 n, - 4,m & = & i\[.3em]
5,n +, 1,m &=& j end{eqnarray}quadRightarrowquad
$ $
begin{align}
23,n &= , i +, 4,j \[.3em]
23,m, &=, -5,i + 3,j end{align} $
Thus by RHS: $,dmid i,j,Rightarrow, dmid 23m,23n,Rightarrow, dmid 23 $ as above. More generally this method yields
Theorem $ $ If $rm,[x,y]overset{A}mapsto [X,Y],$ is linear then $: rm(x,y)mid (X,Y)mid color{#90f}Delta, (x,y), color{#90f}{Delta := {rm det}, A}$
e.g. $ $ in OP we have $,color{#90f}{Delta =bf 23},$ so the above yields $ (3n!-!4m,5n!+!m)midcolor{#90f}{bf 23}(n,m) = 23$
using the map $ [n,m]mapsto [3n!-!4m,,5n!+!m] $ i.e.
$$ [n,,m],mapsto, [n,,m],underbrace{begin{bmatrix}3 & 5\ -4 &1end{bmatrix}}_{large det A, =, color{#90f}{bf 23}} =, [3n!-!4m,,5n!+!m]$$
edited Dec 7 '18 at 20:38
answered Dec 7 '18 at 1:19
Bill DubuqueBill Dubuque
209k29190633
209k29190633
$begingroup$
Thanks for explaining where I went wrong, and then providing more interesting information!
$endgroup$
– Lowkey
Dec 7 '18 at 1:46
add a comment |
$begingroup$
Thanks for explaining where I went wrong, and then providing more interesting information!
$endgroup$
– Lowkey
Dec 7 '18 at 1:46
$begingroup$
Thanks for explaining where I went wrong, and then providing more interesting information!
$endgroup$
– Lowkey
Dec 7 '18 at 1:46
$begingroup$
Thanks for explaining where I went wrong, and then providing more interesting information!
$endgroup$
– Lowkey
Dec 7 '18 at 1:46
add a comment |
$begingroup$
If $m=3$ and $n=4$, the greatest common divisor of $3n-4m=0$ and $5n+m=23$ is $23$.
If $m=1$ and $n=1$, the greatest common divisor of $3n-4m=-1$ and $5n+m=6$ is $1$.
Your argument is good, but the conclusion is wrong: you prove that $d$ can be a divisor of $23$. Thus it is either $1$ or $23$.
$endgroup$
$begingroup$
Thanks, this clears things up.
$endgroup$
– Lowkey
Dec 6 '18 at 23:49
add a comment |
$begingroup$
If $m=3$ and $n=4$, the greatest common divisor of $3n-4m=0$ and $5n+m=23$ is $23$.
If $m=1$ and $n=1$, the greatest common divisor of $3n-4m=-1$ and $5n+m=6$ is $1$.
Your argument is good, but the conclusion is wrong: you prove that $d$ can be a divisor of $23$. Thus it is either $1$ or $23$.
$endgroup$
$begingroup$
Thanks, this clears things up.
$endgroup$
– Lowkey
Dec 6 '18 at 23:49
add a comment |
$begingroup$
If $m=3$ and $n=4$, the greatest common divisor of $3n-4m=0$ and $5n+m=23$ is $23$.
If $m=1$ and $n=1$, the greatest common divisor of $3n-4m=-1$ and $5n+m=6$ is $1$.
Your argument is good, but the conclusion is wrong: you prove that $d$ can be a divisor of $23$. Thus it is either $1$ or $23$.
$endgroup$
If $m=3$ and $n=4$, the greatest common divisor of $3n-4m=0$ and $5n+m=23$ is $23$.
If $m=1$ and $n=1$, the greatest common divisor of $3n-4m=-1$ and $5n+m=6$ is $1$.
Your argument is good, but the conclusion is wrong: you prove that $d$ can be a divisor of $23$. Thus it is either $1$ or $23$.
answered Dec 6 '18 at 23:42
egregegreg
180k1485202
180k1485202
$begingroup$
Thanks, this clears things up.
$endgroup$
– Lowkey
Dec 6 '18 at 23:49
add a comment |
$begingroup$
Thanks, this clears things up.
$endgroup$
– Lowkey
Dec 6 '18 at 23:49
$begingroup$
Thanks, this clears things up.
$endgroup$
– Lowkey
Dec 6 '18 at 23:49
$begingroup$
Thanks, this clears things up.
$endgroup$
– Lowkey
Dec 6 '18 at 23:49
add a comment |
$begingroup$
By Bezout we have $An+Bm=1$, multiply this by $23$ and create some terms
begin{eqnarray*}
20An+4Am-4Am+3An+20Bm-15Bn+15Bn+3Bm=23.
end{eqnarray*}
Now factorise
begin{eqnarray*}
(4A+3B)(m+5n) +(A-5B)(3n-4m) =23.
end{eqnarray*}
So if $(4A+3B,A-5B)=1$ then $(m+5n,3n-4m)=23$ and
and if $(4A+3B,A-5B)=23$ then $(m+5n,3n-4m)=1$.
$endgroup$
add a comment |
$begingroup$
By Bezout we have $An+Bm=1$, multiply this by $23$ and create some terms
begin{eqnarray*}
20An+4Am-4Am+3An+20Bm-15Bn+15Bn+3Bm=23.
end{eqnarray*}
Now factorise
begin{eqnarray*}
(4A+3B)(m+5n) +(A-5B)(3n-4m) =23.
end{eqnarray*}
So if $(4A+3B,A-5B)=1$ then $(m+5n,3n-4m)=23$ and
and if $(4A+3B,A-5B)=23$ then $(m+5n,3n-4m)=1$.
$endgroup$
add a comment |
$begingroup$
By Bezout we have $An+Bm=1$, multiply this by $23$ and create some terms
begin{eqnarray*}
20An+4Am-4Am+3An+20Bm-15Bn+15Bn+3Bm=23.
end{eqnarray*}
Now factorise
begin{eqnarray*}
(4A+3B)(m+5n) +(A-5B)(3n-4m) =23.
end{eqnarray*}
So if $(4A+3B,A-5B)=1$ then $(m+5n,3n-4m)=23$ and
and if $(4A+3B,A-5B)=23$ then $(m+5n,3n-4m)=1$.
$endgroup$
By Bezout we have $An+Bm=1$, multiply this by $23$ and create some terms
begin{eqnarray*}
20An+4Am-4Am+3An+20Bm-15Bn+15Bn+3Bm=23.
end{eqnarray*}
Now factorise
begin{eqnarray*}
(4A+3B)(m+5n) +(A-5B)(3n-4m) =23.
end{eqnarray*}
So if $(4A+3B,A-5B)=1$ then $(m+5n,3n-4m)=23$ and
and if $(4A+3B,A-5B)=23$ then $(m+5n,3n-4m)=1$.
answered Dec 6 '18 at 23:47
Donald SplutterwitDonald Splutterwit
22.4k21344
22.4k21344
add a comment |
add a comment |
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In my understanding your conclusion does not look correct, because $d$ can divide both $m$ and $n$, and in that case it is equal to $1$. Otherwise, it divides $23$, hence it is either $1$ or $23$.
$endgroup$
– Gibbs
Dec 6 '18 at 23:41
$begingroup$
What does $(m/n)$ mean???
$endgroup$
– bof
Dec 6 '18 at 23:42
$begingroup$
I meant the greatest common divisor.
$endgroup$
– Lowkey
Dec 6 '18 at 23:45
$begingroup$
Um don't you mean $d$ must divide $23$. Not $23$ must divide $d$?
$endgroup$
– fleablood
Dec 7 '18 at 1:33