- #1
AlbertEinstein
- 113
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Hi,
I am going through the book on number theory by ivan niven. well its tough book though, and i am stuck with problems in the first topic divisbility.Hope some help.
1. prove that a|bc if and only if a/(b,c)|c where (b,c) is the lcm of b and c.
2. Prove that there are no positive integers a,b,n>1 such that
[tex](a^n-b^n)|(a^n+b^n)[/tex].
In the first one i have no clue how to start the proof. any hint will be appreciated.
In the second one i had the following proof:
if posssible let there be a +ve integer k such that
[tex]\frac{a^n-b^n}{a^n+b^n} = k[/tex]
clearly k is not equal to 1, since then b=0 which is contradictory.
applying compodendo and dividendo to the above frac we write
(a/b)^n = (k+1)/(k-1) ---------------------------(1)
now (k+1)/(k-1) can be written as (1 + 2/(k-1) )
It can be directly checked that k=2,3 do not satisfy (1)
for k>3, (k+1)/(k-1) lies between 1 and 2 and hence cannot be a perfect nth number. this contradiction gives the desired proof.
well,are my lines of reasoning true?
I am going through the book on number theory by ivan niven. well its tough book though, and i am stuck with problems in the first topic divisbility.Hope some help.
1. prove that a|bc if and only if a/(b,c)|c where (b,c) is the lcm of b and c.
2. Prove that there are no positive integers a,b,n>1 such that
[tex](a^n-b^n)|(a^n+b^n)[/tex].
In the first one i have no clue how to start the proof. any hint will be appreciated.
In the second one i had the following proof:
if posssible let there be a +ve integer k such that
[tex]\frac{a^n-b^n}{a^n+b^n} = k[/tex]
clearly k is not equal to 1, since then b=0 which is contradictory.
applying compodendo and dividendo to the above frac we write
(a/b)^n = (k+1)/(k-1) ---------------------------(1)
now (k+1)/(k-1) can be written as (1 + 2/(k-1) )
It can be directly checked that k=2,3 do not satisfy (1)
for k>3, (k+1)/(k-1) lies between 1 and 2 and hence cannot be a perfect nth number. this contradiction gives the desired proof.
well,are my lines of reasoning true?
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