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Here is a nice old school question. "Legendary" question

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Thread replies: 13
Thread images: 1

Here is a nice old school question. "Legendary" question 6 from the junior maths tournament of 1988.

Let a and b be positive integers in the equation (a^2 + b^2)/(ab+1). Show that this equation is the square of an integer.

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If you cant do it dont fret not many can, but what are your ideas about these type of questions that take 2 variables and "push" them into a 3D sense?
>>
>>8795875
a=3
b=4
(a^2 + b^2)/(ab+1) = 25/13
>Show that this equation is the square of an integer.
???
>>
let
a=1
b=1
(a^2 + b^2)/(ab+1) = 2/2 = 1
1^2=1
>>
>>8795895
Square of an integer almost means 2^n so sub in a = 0 and b = 2 and u get 4 which is 2^2 aswell
>>
>>8795935
Keep going
>>
>>8795875
Looks like Vieta jumping might work.
>>
>>8795937
what???

(a^2+b^2)/(ab+1) is not always the square of an integer, so the question of the OP is retarded, and false.
>>
>>8796023

Wikipedia Vieta jumping
>>
>>8796023
>>8795937
>>8796023
>>8795895
I found what OP means, he can't even copy a fucking question right, let alone find the solution.

Show that if a, b and n=(a^2+b^2)/(ab+1) are integers, then n is also the square of an integer.
>>
>>8796024
no thanks, I'd rather derive it myself.
>>
>>8795875
for the case b = a^3 we have
(a^2+b^2)/(ab+1) = (a^2+a^6)/(a^4+1) = a^2(1+a^4)/(1+a^4) = a^2
unfortunately this doesn't cover all cases
>>
>>8796325
spoken like a true mathematician
>>
>>8796325
kek
Thread posts: 13
Thread images: 1


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