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How many positive integer solutions does x 2 + y 2 = z 3 x^{2} + y^{2} = z^{3} has?

Finite Infinite 0

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3 solutions

Jon Haussmann
Mar 2, 2016

For any nonnegative integer k k , ( x , y , z ) = ( 2 3 k + 1 , 2 3 k + 1 , 2 2 k + 1 ) (x,y,z) = (2^{3k + 1}, 2^{3k + 1}, 2^{2k + 1}) is a solution. Thus, there are an infinite number of solutions.

Kay Xspre
Mar 1, 2016

The very most obvious is for the case of ( x , y , z ) = ( 75 , 100 , 25 ) , ( 26 , 18 , 10 ) (x, y, z) = (75, 100, 25), (26, 18, 10) and some others like ( 9600 , 280 , 100 ) (9600, 280, 100)

Raushan Sharma
Apr 15, 2016

Take x = a ( a 2 + b 2 ) , y = b ( a 2 + b 2 ) , z = ( a 2 + b 2 ) x = a(a^2 + b^2), y = b(a^2 + b^2), z = (a^2 + b^2) for any a , b N a,b \in \mathbb N .

Then, LHS = x 2 + y 2 = a 2 ( a 2 + b 2 ) 2 + b 2 ( a 2 + b 2 ) 2 = ( a 2 + b 2 ) 3 = z 3 x^2 + y^2 = a^2(a^2 + b^2)^2 + b^2(a^2 + b^2)^2 = (a^2 + b^2)^3 = z^3 .

Hence, there are infinitely many solutions.

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