Verification for a Proof By Contradiction concerning a 5-root being irrational The Next CEO of...
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Verification for a Proof By Contradiction concerning a 5-root being irrational
The Next CEO of Stack OverflowProof that the set of irrational numbers is dense in realsThe square root of a prime number is irrationalUnderstanding the proof of “$sqrt{2}$ is irrational” by contradiction.Why do we consider that $p$ & $q$ are co-primes when proving square root of a prime number is irrational?Proof by contradictionPlease critique my proof that $sqrt{12}$ is irrationalProof that, for every positive integer $n$, $log_7(n)$ is either integer or irrationalIs this a valid proof for $sqrt5$ being irrational?Is this proof of $sqrt{3}$ being an irrational number correct?Proof by contradiction that an expression is irrational
$begingroup$
I was asked to prove that for a non negative $m$ number, that is not a 5-th power of an integer, its 5-root, $sqrt[5]m$ is not a rational number.
Thanks for any feedback.
Proof By Contradiction:
Suppose Not,
Assume that for a non-negative $m$ number, that is not a 5-th power of an integer, its 5-root $sqrt[5]m$ is a rational number.
Being a rational number we can say:$$sqrt[5]m=frac{p}{q}quad text{for} ;p,qinBbb{Z};text{and}:qneq0$$
Then by algebra,$$m=left(frac{p}{q}right)^{5}Rightarrow m=frac{p^{5}}{q^{5}}$$
Consider when $frac{p}{q}=n$, $n inBbb Z$,
This is a contradiction with the fact that $m$ is not a 5-th power of an integer.
Hence, $sqrt[5]{m}$ is not a rational number.
real-analysis proof-verification
$endgroup$
add a comment |
$begingroup$
I was asked to prove that for a non negative $m$ number, that is not a 5-th power of an integer, its 5-root, $sqrt[5]m$ is not a rational number.
Thanks for any feedback.
Proof By Contradiction:
Suppose Not,
Assume that for a non-negative $m$ number, that is not a 5-th power of an integer, its 5-root $sqrt[5]m$ is a rational number.
Being a rational number we can say:$$sqrt[5]m=frac{p}{q}quad text{for} ;p,qinBbb{Z};text{and}:qneq0$$
Then by algebra,$$m=left(frac{p}{q}right)^{5}Rightarrow m=frac{p^{5}}{q^{5}}$$
Consider when $frac{p}{q}=n$, $n inBbb Z$,
This is a contradiction with the fact that $m$ is not a 5-th power of an integer.
Hence, $sqrt[5]{m}$ is not a rational number.
real-analysis proof-verification
$endgroup$
1
$begingroup$
Your attempt stops making sense to me after $m=p^5/q^5$.
$endgroup$
– learner
Mar 16 at 5:27
1
$begingroup$
How can you be sure that $frac{p}{q}$ will be an integer $n$?
$endgroup$
– Sujit Bhattacharyya
Mar 16 at 5:30
1
$begingroup$
It's not quite that easy. For all you know, $mq^5$ could be the fifth power of an integer even though $m$ is not. You need to use the prime factorization of $m$, just as is done to prove $sqrt{2}$ is irrational.
$endgroup$
– Robert Shore
Mar 16 at 5:31
add a comment |
$begingroup$
I was asked to prove that for a non negative $m$ number, that is not a 5-th power of an integer, its 5-root, $sqrt[5]m$ is not a rational number.
Thanks for any feedback.
Proof By Contradiction:
Suppose Not,
Assume that for a non-negative $m$ number, that is not a 5-th power of an integer, its 5-root $sqrt[5]m$ is a rational number.
Being a rational number we can say:$$sqrt[5]m=frac{p}{q}quad text{for} ;p,qinBbb{Z};text{and}:qneq0$$
Then by algebra,$$m=left(frac{p}{q}right)^{5}Rightarrow m=frac{p^{5}}{q^{5}}$$
Consider when $frac{p}{q}=n$, $n inBbb Z$,
This is a contradiction with the fact that $m$ is not a 5-th power of an integer.
Hence, $sqrt[5]{m}$ is not a rational number.
real-analysis proof-verification
$endgroup$
I was asked to prove that for a non negative $m$ number, that is not a 5-th power of an integer, its 5-root, $sqrt[5]m$ is not a rational number.
Thanks for any feedback.
Proof By Contradiction:
Suppose Not,
Assume that for a non-negative $m$ number, that is not a 5-th power of an integer, its 5-root $sqrt[5]m$ is a rational number.
Being a rational number we can say:$$sqrt[5]m=frac{p}{q}quad text{for} ;p,qinBbb{Z};text{and}:qneq0$$
Then by algebra,$$m=left(frac{p}{q}right)^{5}Rightarrow m=frac{p^{5}}{q^{5}}$$
Consider when $frac{p}{q}=n$, $n inBbb Z$,
This is a contradiction with the fact that $m$ is not a 5-th power of an integer.
Hence, $sqrt[5]{m}$ is not a rational number.
real-analysis proof-verification
real-analysis proof-verification
asked Mar 16 at 5:18
MACMAC
283
283
1
$begingroup$
Your attempt stops making sense to me after $m=p^5/q^5$.
$endgroup$
– learner
Mar 16 at 5:27
1
$begingroup$
How can you be sure that $frac{p}{q}$ will be an integer $n$?
$endgroup$
– Sujit Bhattacharyya
Mar 16 at 5:30
1
$begingroup$
It's not quite that easy. For all you know, $mq^5$ could be the fifth power of an integer even though $m$ is not. You need to use the prime factorization of $m$, just as is done to prove $sqrt{2}$ is irrational.
$endgroup$
– Robert Shore
Mar 16 at 5:31
add a comment |
1
$begingroup$
Your attempt stops making sense to me after $m=p^5/q^5$.
$endgroup$
– learner
Mar 16 at 5:27
1
$begingroup$
How can you be sure that $frac{p}{q}$ will be an integer $n$?
$endgroup$
– Sujit Bhattacharyya
Mar 16 at 5:30
1
$begingroup$
It's not quite that easy. For all you know, $mq^5$ could be the fifth power of an integer even though $m$ is not. You need to use the prime factorization of $m$, just as is done to prove $sqrt{2}$ is irrational.
$endgroup$
– Robert Shore
Mar 16 at 5:31
1
1
$begingroup$
Your attempt stops making sense to me after $m=p^5/q^5$.
$endgroup$
– learner
Mar 16 at 5:27
$begingroup$
Your attempt stops making sense to me after $m=p^5/q^5$.
$endgroup$
– learner
Mar 16 at 5:27
1
1
$begingroup$
How can you be sure that $frac{p}{q}$ will be an integer $n$?
$endgroup$
– Sujit Bhattacharyya
Mar 16 at 5:30
$begingroup$
How can you be sure that $frac{p}{q}$ will be an integer $n$?
$endgroup$
– Sujit Bhattacharyya
Mar 16 at 5:30
1
1
$begingroup$
It's not quite that easy. For all you know, $mq^5$ could be the fifth power of an integer even though $m$ is not. You need to use the prime factorization of $m$, just as is done to prove $sqrt{2}$ is irrational.
$endgroup$
– Robert Shore
Mar 16 at 5:31
$begingroup$
It's not quite that easy. For all you know, $mq^5$ could be the fifth power of an integer even though $m$ is not. You need to use the prime factorization of $m$, just as is done to prove $sqrt{2}$ is irrational.
$endgroup$
– Robert Shore
Mar 16 at 5:31
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
Well, you are on the right track, but you cannot consider when $p/q = n in mathbb Z$.
HINT
I guess you implicitly meant that $m$ is a non-negative integer. Then, we have:
$q^5 cdot m = p^5$, where $m, q, p$ are non-negative integers, and $p$, $q$ are coprime with each other, or $p=1$ or $q=1$.
Can you continue?
$endgroup$
$begingroup$
Are you saying that from the fact m exists in Z+ and m>0, p,q >0,and that we can define p,q as coprime with each other. From this we have two cases: where p=1, or q=1?
$endgroup$
– MAC
Mar 20 at 1:23
1
$begingroup$
@MAC No, I mean since p/q is a rational number, then q,p are either coprime; or q = 1; or p = 1. For each scenario, you could check for your equation, and you’ll find that only when q=1 will make you equation solvable, but in that case, m is 5-th power of an integer
$endgroup$
– Yujie Zha
Mar 20 at 1:26
add a comment |
$begingroup$
You may assume (wlog) that $qgt 0$, so since $p^5/q^5=minBbb Z$, this implies $q^5mid p^5$. You can furthermore assume (wlog) that $gcd(p,q)=1$. This would imply that $qmid p$, so $1=gcd(p,q)=q$ but then $m=p^5$ leading to a contradiction that $m$ is a 5th power of an integer, namely $p$
In fact, this argument can be generalized to $sqrt[n]m$ where $m$ is not a perfect $n^text{th}$ power
$endgroup$
add a comment |
Your Answer
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2 Answers
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active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
Well, you are on the right track, but you cannot consider when $p/q = n in mathbb Z$.
HINT
I guess you implicitly meant that $m$ is a non-negative integer. Then, we have:
$q^5 cdot m = p^5$, where $m, q, p$ are non-negative integers, and $p$, $q$ are coprime with each other, or $p=1$ or $q=1$.
Can you continue?
$endgroup$
$begingroup$
Are you saying that from the fact m exists in Z+ and m>0, p,q >0,and that we can define p,q as coprime with each other. From this we have two cases: where p=1, or q=1?
$endgroup$
– MAC
Mar 20 at 1:23
1
$begingroup$
@MAC No, I mean since p/q is a rational number, then q,p are either coprime; or q = 1; or p = 1. For each scenario, you could check for your equation, and you’ll find that only when q=1 will make you equation solvable, but in that case, m is 5-th power of an integer
$endgroup$
– Yujie Zha
Mar 20 at 1:26
add a comment |
$begingroup$
Well, you are on the right track, but you cannot consider when $p/q = n in mathbb Z$.
HINT
I guess you implicitly meant that $m$ is a non-negative integer. Then, we have:
$q^5 cdot m = p^5$, where $m, q, p$ are non-negative integers, and $p$, $q$ are coprime with each other, or $p=1$ or $q=1$.
Can you continue?
$endgroup$
$begingroup$
Are you saying that from the fact m exists in Z+ and m>0, p,q >0,and that we can define p,q as coprime with each other. From this we have two cases: where p=1, or q=1?
$endgroup$
– MAC
Mar 20 at 1:23
1
$begingroup$
@MAC No, I mean since p/q is a rational number, then q,p are either coprime; or q = 1; or p = 1. For each scenario, you could check for your equation, and you’ll find that only when q=1 will make you equation solvable, but in that case, m is 5-th power of an integer
$endgroup$
– Yujie Zha
Mar 20 at 1:26
add a comment |
$begingroup$
Well, you are on the right track, but you cannot consider when $p/q = n in mathbb Z$.
HINT
I guess you implicitly meant that $m$ is a non-negative integer. Then, we have:
$q^5 cdot m = p^5$, where $m, q, p$ are non-negative integers, and $p$, $q$ are coprime with each other, or $p=1$ or $q=1$.
Can you continue?
$endgroup$
Well, you are on the right track, but you cannot consider when $p/q = n in mathbb Z$.
HINT
I guess you implicitly meant that $m$ is a non-negative integer. Then, we have:
$q^5 cdot m = p^5$, where $m, q, p$ are non-negative integers, and $p$, $q$ are coprime with each other, or $p=1$ or $q=1$.
Can you continue?
answered Mar 16 at 5:36
Yujie ZhaYujie Zha
6,98611729
6,98611729
$begingroup$
Are you saying that from the fact m exists in Z+ and m>0, p,q >0,and that we can define p,q as coprime with each other. From this we have two cases: where p=1, or q=1?
$endgroup$
– MAC
Mar 20 at 1:23
1
$begingroup$
@MAC No, I mean since p/q is a rational number, then q,p are either coprime; or q = 1; or p = 1. For each scenario, you could check for your equation, and you’ll find that only when q=1 will make you equation solvable, but in that case, m is 5-th power of an integer
$endgroup$
– Yujie Zha
Mar 20 at 1:26
add a comment |
$begingroup$
Are you saying that from the fact m exists in Z+ and m>0, p,q >0,and that we can define p,q as coprime with each other. From this we have two cases: where p=1, or q=1?
$endgroup$
– MAC
Mar 20 at 1:23
1
$begingroup$
@MAC No, I mean since p/q is a rational number, then q,p are either coprime; or q = 1; or p = 1. For each scenario, you could check for your equation, and you’ll find that only when q=1 will make you equation solvable, but in that case, m is 5-th power of an integer
$endgroup$
– Yujie Zha
Mar 20 at 1:26
$begingroup$
Are you saying that from the fact m exists in Z+ and m>0, p,q >0,and that we can define p,q as coprime with each other. From this we have two cases: where p=1, or q=1?
$endgroup$
– MAC
Mar 20 at 1:23
$begingroup$
Are you saying that from the fact m exists in Z+ and m>0, p,q >0,and that we can define p,q as coprime with each other. From this we have two cases: where p=1, or q=1?
$endgroup$
– MAC
Mar 20 at 1:23
1
1
$begingroup$
@MAC No, I mean since p/q is a rational number, then q,p are either coprime; or q = 1; or p = 1. For each scenario, you could check for your equation, and you’ll find that only when q=1 will make you equation solvable, but in that case, m is 5-th power of an integer
$endgroup$
– Yujie Zha
Mar 20 at 1:26
$begingroup$
@MAC No, I mean since p/q is a rational number, then q,p are either coprime; or q = 1; or p = 1. For each scenario, you could check for your equation, and you’ll find that only when q=1 will make you equation solvable, but in that case, m is 5-th power of an integer
$endgroup$
– Yujie Zha
Mar 20 at 1:26
add a comment |
$begingroup$
You may assume (wlog) that $qgt 0$, so since $p^5/q^5=minBbb Z$, this implies $q^5mid p^5$. You can furthermore assume (wlog) that $gcd(p,q)=1$. This would imply that $qmid p$, so $1=gcd(p,q)=q$ but then $m=p^5$ leading to a contradiction that $m$ is a 5th power of an integer, namely $p$
In fact, this argument can be generalized to $sqrt[n]m$ where $m$ is not a perfect $n^text{th}$ power
$endgroup$
add a comment |
$begingroup$
You may assume (wlog) that $qgt 0$, so since $p^5/q^5=minBbb Z$, this implies $q^5mid p^5$. You can furthermore assume (wlog) that $gcd(p,q)=1$. This would imply that $qmid p$, so $1=gcd(p,q)=q$ but then $m=p^5$ leading to a contradiction that $m$ is a 5th power of an integer, namely $p$
In fact, this argument can be generalized to $sqrt[n]m$ where $m$ is not a perfect $n^text{th}$ power
$endgroup$
add a comment |
$begingroup$
You may assume (wlog) that $qgt 0$, so since $p^5/q^5=minBbb Z$, this implies $q^5mid p^5$. You can furthermore assume (wlog) that $gcd(p,q)=1$. This would imply that $qmid p$, so $1=gcd(p,q)=q$ but then $m=p^5$ leading to a contradiction that $m$ is a 5th power of an integer, namely $p$
In fact, this argument can be generalized to $sqrt[n]m$ where $m$ is not a perfect $n^text{th}$ power
$endgroup$
You may assume (wlog) that $qgt 0$, so since $p^5/q^5=minBbb Z$, this implies $q^5mid p^5$. You can furthermore assume (wlog) that $gcd(p,q)=1$. This would imply that $qmid p$, so $1=gcd(p,q)=q$ but then $m=p^5$ leading to a contradiction that $m$ is a 5th power of an integer, namely $p$
In fact, this argument can be generalized to $sqrt[n]m$ where $m$ is not a perfect $n^text{th}$ power
answered Mar 16 at 5:37
learnerlearner
1,110417
1,110417
add a comment |
add a comment |
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1
$begingroup$
Your attempt stops making sense to me after $m=p^5/q^5$.
$endgroup$
– learner
Mar 16 at 5:27
1
$begingroup$
How can you be sure that $frac{p}{q}$ will be an integer $n$?
$endgroup$
– Sujit Bhattacharyya
Mar 16 at 5:30
1
$begingroup$
It's not quite that easy. For all you know, $mq^5$ could be the fifth power of an integer even though $m$ is not. You need to use the prime factorization of $m$, just as is done to prove $sqrt{2}$ is irrational.
$endgroup$
– Robert Shore
Mar 16 at 5:31