Number Theory Problem 1

If x x and y y are 2 positive integers such that x 2 y 2 = 37 x^{2} - y^{2} = 37 , find x + 2 y x +2y .


The answer is 55.

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3 solutions

William Isoroku
Jan 5, 2015

Factoring gives us ( x + y ) ( x y ) = 37 (x+y)(x-y)=37

Since x x and y y are positive and 37 37 is prime, we have:

x + y = 37 x+y=37

x y = 1 x-y=1

Therefore x = 19 x=19 and y = 18 y=18

Deepak Pargain
Jan 5, 2015

difference of 2 consecutive number's squares are in sequence 1,3,5,7,9..... so, let x & y are 2 positive consecutive numbers. so, x=y+1, x^2-y^2=37, (x-y)(x+y)=37, so 2y+1=37, y=18, so, x+2y=55

x 2 y 2 = 37 ( x + y ) ( x y ) = 37 \begin{aligned} x^2-y^2&=37 \\ (x+y)(x-y)&=37 \\ \end{aligned}

x x and y y are 2 2 positive integers.

x + y = 37 x y = 1 x = 19 y = 18 x + 2 y = 19 + 2 ( 18 ) = 19 + 36 = 55 \begin{aligned} x+y&=37 \\ x-y&=1 \\ \implies x&=19 \\ y&=18 \\ \implies x+2y&=19+2(18)=19+36=\boxed{55} \\ \end{aligned}

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