Repeated Substitution

2 x 2 3 y 2 = 2014 2x^{2}-3y^{2}=2014

How many integer solution(s) are possible for the equation above?

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The answer is 0.

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2 solutions

Adarsh Kumar
Oct 15, 2014

The equation given to us is 2 x 2 3 y 2 = 2014. 2x^{2}-3y^{2}=2014. Now, 2 x 2 2x^{2} =even and 2014 = 2014= even.Thus, 3 y 2 = 3y^{2}= even y 2 = \Longrightarrow y^{2}= even y = \Longrightarrow y= even.Let us say that x = ( 2 b + 1 ) , y = 2 a . x=(2b+1),y=2a. Plugging that into the equation given,we get : 2 ( 2 b + 1 ) 2 3 ( 4 a 2 ) = 2014. :2(2b+1)^{2}-3(4a^{2})=2014. Simplifying gives 8 b 2 + 2 + 8 b 12 a 2 = 2014. 8b^{2}+2+8b-12a^{2}=2014. This gives, 8 b ( b 1 ) 12 a 2 = 2012 2 b ( b 1 ) 3 a 2 = 503 8b(b-1)-12a^{2}=2012\Longrightarrow 2b(b-1)-3a^{2}=503 (dividing by 4).This gives that 3 a 2 = 3a^{2}= odd. a = \Longrightarrow a= odd.Taking a = 2 c + 1 a=2c+1 gives 2 b 2 + 2 b 12 c 2 3 12 c = 503. 2b^{2}+2b-12c^{2}-3-12c=503. 2 ( b 2 + b 6 c 2 6 c = 506. \Longrightarrow 2(b^{2}+b-6c^{2}-6c=506. This simplifies to b ( b + 1 ) 6 c ( c + 1 ) = 253. b(b+1)-6c(c+1)=253. But this can't happen as b ( b + 1 ) = b(b+1)= even.Because the product of two consecutive numbers is always even.Obviously, 6 c ( c + 1 ) = 6c(c+1)= even.But even-even=even.Thus,the answer is 0. 0.

Nice solution! :)

Curtis Clement - 6 years, 4 months ago

@Anik Mandal

Adarsh Kumar - 6 years, 8 months ago

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What happened?

Anik Mandal - 6 years, 7 months ago

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Nothing,I just wanted you to see my solution.:)

Adarsh Kumar - 6 years, 7 months ago

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@Adarsh Kumar It's good!!

Anik Mandal - 6 years, 7 months ago

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@Anik Mandal Thanx a lot!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Adarsh Kumar - 6 years, 7 months ago

2 x 2 3 y 2 = 2014 3 2 y 2 = 1007 x 2 y 2 = ( 1007 x 2 ) ( 2 3 ) ( x 2 1007 ) ( 2 ) 3 = y 2 2 2 ( m o d 3 ) x 2 2 ( m o d 3 ) B u t t h i s i s i m p o s s i b l e . x 2 c a n o n l y b e i d e n t i c a l t o 0 o r 1. T h e r e f o r e , t h e r e a r e n o s u c h v a l u e s . 2{ x }^{ 2 }-3{ y }^{ 2 }=2014\\ \frac { -3 }{ 2 } { y }^{ 2 }=1007-{ x }^{ 2 }\\ { y }^{ 2 }=(1007-x^{ 2 })(\frac { -2 }{ 3 } )\\ \therefore \frac { (x^{ 2 }-1007)(2) }{ 3 } ={ y }^{ 2 }\\ 2\quad \equiv \quad 2\quad (mod\quad 3)\\ \therefore \quad x^{ 2 }\quad \equiv \quad 2\quad (mod\quad 3)\\ But\quad this\quad is\quad impossible.\quad x^{ 2 }\quad can\quad only\quad be\quad identical\quad to\quad 0\quad or\quad 1.\\ Therefore,\quad there\quad are\quad no\quad such\quad values.

or, if code is not displaying, https://drive.google.com/file/d/0B42CxY5sovrLdWtrOWhOWWpleDQ/view?usp=sharing

Could you explain the last 2 steps .

The one in which you used Mod

Rajdeep Dhingra - 6 years, 4 months ago

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