An 'identitial' problem

The number of pairs of positive integers ( x , y ) (x,y) satisfying the equation:

x 2 + y 2 + 2 x y 2008 x 2008 y 2009 = 0 are x^2+y^2+2xy-2008x-2008y-2009=0\space \text{are}

2009 2011 2008 2010

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1 solution

Aaryan Maheshwari
Sep 11, 2017

x 2 + y 2 + 2 x y 2008 x 2008 y 2009 = 0 x^2+y^2+2xy-2008x-2008y-2009=0 ( x + y ) 2 = 2008 x + 2008 y + 2009 \Rightarrow(x+y)^2=2008x+2008y+2009 ( x + y ) 2 = 2008 ( x + y ) + 2008 + 1 \Rightarrow(x+y)^2=2008(x+y)+2008+1 ( x + y ) 2 1 2 = 2008 ( x + y + 1 ) \Rightarrow(x+y)^2-1^2=2008(x+y+1) ( x + y + 1 ) ( x + y 1 ) = 2008 ( x + y + 1 ) \Rightarrow(x+y+1)(x+y-1)=2008(x+y+1) x + y = 2009 \Rightarrow\boxed{x+y=2009} The solutions are:

x = 1 , y = 2008 x=1,y=2008 x = 2 , y = 2007........... and so on till x = 2008 , y = 1 x=2,y=2007...........\space \text{and so on till}\space x=2008,y=1

\therefore\space Total number of solutions = 2008 1 1 + 1 = 2008 . =\large\frac{2008-1}{1}+1=\boxed{2008}.

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