Symmetrically paired equation

Find the number of integer pairs ( x , y ) (x,y) such that x 3 ( y + 1 ) + y 3 ( x + 1 ) = 19 x^3(y+1)+y^3(x+1)=19


The answer is 4.

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1 solution

Alexander Shannon
Nov 22, 2020

Obviously, none of x , y x,y can be equal to zero. If one of x , y x,y is positive and the other is negative, then the LHS is negative (no solution). Both x , y x,y should be either positive or negative, which automatically impose limits on the absolute values of them ( m i n ( x , y ) 2 min(|x|,|y|) \leq 2 ). The rest is just trying a couple of integers in the mentioned ranged considering symmetry of the equation, wrt x x and y y . The pairs are ( 1 , 2 ) (1,2) , ( 2 , 1 ) (2,1) , ( 1 , 20 ) (-1,-20) ,and ( 20 , 1 ) (-20,-1)

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