Part 10

Let x > y x>y be positive integers satisfying x + y = 2016 \sqrt x + \sqrt y = \sqrt{2016} , with x x not divisible by y y . Find x + y x+y .


The answer is 1036.

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2 solutions

Since 2016 = 2 5 3 2 7 2016 = 2^{5}*3^{2}*7 the equation can be written as x + y = 12 14 \sqrt{x} + \sqrt{y} = 12\sqrt{14} .

With x = 14 n 2 , y = 14 m 2 x = 14n^{2}, y = 14m^{2} for integers 0 < m < n 0 \lt m \lt n the equation becomes

n 14 + m 14 = 12 14 n + m = 12 n\sqrt{14} + m\sqrt{14} = 12\sqrt{14} \Longrightarrow n + m = 12 .

This gives us the possible pairings ( n , m ) = ( 11 , 1 ) , ( 10 , 2 ) , ( 9 , 3 ) , ( 8 , 4 ) (n,m) = (11,1), (10,2), (9,3), (8,4) and ( 7 , 5 ) (7,5) , the only one of which has m m not dividing n n being ( 7 , 5 ) (7,5) . Thus x + y = 14 ( 7 2 + 5 2 ) = 1036 x + y = 14*(7^{2} + 5^{2}) = \boxed{1036} .

Son Nguyen
Jan 16, 2016

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Akhash Raja Raam - 5 years ago

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Akhash Raja Raam - 5 years ago

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