2014 is somewhat special

How many triplets of integers ( a , b , c ) (a, b, c) are there such that a 4 + b 4 + c 4 = 2 a 2 b 2 + 2 b 2 c 2 + 2 c 2 a 2 + 2014 ? a^4 + b^4 + c^4 = 2 a^2b^2 + 2 b^2c^2 + 2 c^2a^2 + 2014?


The answer is 0.

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9 solutions

a 4 + b 4 + c 4 2 a 2 b 2 2 b 2 c 2 2 a 2 c 2 = 2014 a^4 + b^4 + c^4 - 2a^2b^2 - 2b^2c^2 - 2a^2c^2 = 2014

( a 2 + b 2 ) 2 4 a 2 b 2 + c 4 2 c 2 ( a 2 + b 2 ) = 2014 (a^2 + b^2)^2 - 4a^2b^2 + c^4 -2c^2(a^2 + b^2) = 2014

( a 2 + b 2 c 2 ) 2 4 a 2 b 2 = 2014 (a^2 + b^2 -c^2)^2 - 4a^2b^2 = 2014

( a 2 + b 2 c 2 2 a b ) ( a 2 + b 2 c 2 + 2 a b ) = 2014 (a^2 + b^2 - c^2 - 2ab)(a^2 + b^2 -c^2 + 2ab) = 2014

Suppose there are integer solutions.

Now, since 2014 = 2 × 1007 2014 = 2 \times 1007 , one and only one of the terms must be divisible by 2 2 . But since the terms differ by 4 a b 4ab , if one term is divisible by 2, the other term MUST be divisble by 2, which leads to a contradiction. Therefore, there exist no integer solutions and the answer is 0 \boxed{0}

good solution

Sahil Gohan - 7 years, 2 months ago

"BRILLIANT" Solution

Priyansh Sangule - 7 years, 2 months ago

exactly how i did it!

Shikhar Jaiswal - 7 years, 2 months ago

Smart way :)

Mahtab Hossain - 6 years ago
Abhishek Sinha
Mar 13, 2014

Observation : The right hand side of the given equation is even. Hence the left hand side must also be even. This gives rise to two cases.

Case 1 : a,b,c are all even. In that case a 4 + b 4 + c 4 2 a 2 b 2 2 b 2 c 2 2 c 2 a 2 a^4+b^4+c^4-2a^2b^2-2b^2c^2-2c^2a^2 is divisible by 16, while 2014 is not. Hence this case is not possible.

Case 2: two of a,b,c are odd, the other one is even. Without any loss of generality, assume a a and b b are odd. Then it is easy to verify that a 2 = 1 m o d ( 4 ) , b 2 = 1 m o d ( 4 ) , c 2 = 0 m o d ( 4 ) a^2=1\mod(4),b^2=1 \mod (4), c^2=0 \mod(4) . Hence a 4 + b 4 + c 4 2 a 2 b 2 2 b 2 c 2 2 c 2 a 2 m o d ( 4 ) = 0 a^4+b^4+c^4-2a^2b^2-2b^2c^2-2c^2a^2 \mod(4)=0 , while 2014 is not divisible by 4. Hence this case is also not possible.

Thus there does not exist any solution to this diophantine equation. \blacksquare

wll done meet me

Anshu Jha - 7 years, 2 months ago
Pi Han Goh
Mar 13, 2014

Suppose there's a solution, because variable are replaceable with their additive inverse, then without the loss of the generality, we may assume that 0 a b c 0 \leq a \leq b \leq c

If a = 0 a = 0 , rearrange the equation and we get ( c 2 b 2 ) 2 = 2014 (c^2-b^2)^2 = 2014 , which doesn't have integer solution because 2014 2014 is not a perfect square. So they are all positive integers.

Because 1 + 1 + 1 a 4 + b 4 + c 4 2014 < 7 4 1+1+1 \leq a^4 + b^4 + c^4 \leq 2014 < 7^4 , we have 1 a b c 6 1 \leq a \leq b \leq c \leq 6

Since 2 2 divides RHS \text{RHS} , if we have all three of a , b , c a,b,c are even numbers, then 2 4 2^4 divides LHS \text{LHS} but doesn't divide RHS \text{RHS} , which is absurd. So the triplets ( a , b , c ) (a,b,c) must have two odd numbers and one even number.

Noting that one of the variation of Heron's Formula is, Area = 1 4 2 ( a 2 b 2 + a 2 c 2 + b 2 c 2 ) ( a 4 + b 4 + c 4 ) \text{Area } = \frac {1}{4} \sqrt{ 2\left (a^2 b^2+ a^2 c^2+b^2 c^2 \right) - \left (a^4 + b^4 + c^4 \right ) }

If we assume a , b , c a,b,c are lengths of the triangle (possible degenerate triangle), then the area of the triangle is 2014 4 \frac {\sqrt{-2014}}{4} which is invalid. So they can't be the lengths of a triangle. Thus, we have another constraint a + b < c a+b<c

So with constraints:

  • 1 a b c 6 1 \leq a \leq b \leq c \leq 6 ,

  • the triplets ( a , b , c ) (a,b,c) must have two odd numbers and one even number.

  • a + b < c a+b < c

there's only a couple of trial and errors we need to carry out to determine whether they satisfy the given equation

( 1 , 1 , 4 ) Invalid Solution (1,1,4) \Rightarrow \text{ Invalid Solution}

( 1 , 1 , 6 ) Invalid Solution (1,1,6) \Rightarrow \text{ Invalid Solution}

( 1 , 2 , 5 ) Invalid Solution (1,2,5) \Rightarrow \text{ Invalid Solution}

( 1 , 3 , 6 ) Invalid Solution (1,3,6) \Rightarrow \text{ Invalid Solution}

Since we have exhausted all possible scenario, there's no integer solution to the given equation.

u made it difficult....be easy....

Hitman 47 - 7 years, 2 months ago

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THAT'S MY TALENT!

Pi Han Goh - 7 years, 2 months ago

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True elegence lies in making things simpler. I can employ a really long solution based on further breaking up terms on both sides and evaluating all 4! ways. (I began doing it that way and got fed up and gave up. I tried zero and hurray!!!)

Satyam Bhardwaj - 7 years, 2 months ago

What a saying, Han

Reazul Zannat - 7 years, 2 months ago
Eddie The Head
Apr 5, 2014

a 4 + b 4 + c 4 = 2 a 2 b 2 + 2 b 2 c 2 + 2 c 2 a 2 + 2014 a^{4} + b^{4} + c^{4} = 2a^{2}b^{2}+2b^{2}c^{2}+2c^{2}a^{2}+2014 This can be written as ( a + b + c ) ( c a b ) ( c a + b ) ( c + a b ) = 2014 (a+b+c)(c-a-b)(c-a+b)(c+a-b) = 2014 ( a + b + c ) ( c a b ) ( c a + b ) ( c + a b ) = 2 19 53 (a+b+c)(c-a-b)(c-a+b)(c+a-b) = 2*19*53 So one of the 4 terms is even. But we see that ( a + b + c ) ( c + a + b ) ) = 2 ( a + b ) (a+b+c)-(c+a+b)) = 2(a+b) and ( c a + b ) ( c + a b ) = 2 ( a b ) (c-a+b)-(c+a-b) = 2(a-b) . So if one is even the other term must also be even but two terms cannot be even as 2014 contains only one 2 in it's prime factors....Hence no solutions are possible....

Muhammad Shariq
Mar 27, 2014

It doesn't take long to notice that bringing all the terms, except 2014, to the left-hand-side, the expression can be factored as:

( a 2 b 2 c 2 ) 2 = 2014 (a^2-b^2-c^2)^2=2014 .

We make this observation by noting that ( a + b + c ) 2 = a 2 + b 2 + c 2 + 2 ( a b + b c + c a ) (a+b+c)^2 = a^2+b^2+c^2 + 2(ab+bc+ca) . Similarly, if we have 2 a b , 2 b c , 2 c a -2ab,-2bc,-2ca instead, the factorisation simply becomes ( a b c ) 2 (a-b-c)^2 .

From this observation, we take the square-roots of both sides and bring c 2 c^2 over to the right-hand-side:

a 2 b 2 = c 2 ± 2014 \implies a^2-b^2 = c^2 \pm \sqrt{2014} .

Now note that a a and b b are both integers hence the L.H.S is always an integer. On the R.H.S, c 2 c^2 is always an integer but 2014 Z \sqrt{2014} \notin \mathbb{Z} , therefore the R.H.S is never an integer. Hence the number of solutions to this equation is trivially 0 . \boxed{0}.

muhammad shariq , i think you made a wrong assumption there. (a^2-b^2-C^2)^2 is not correct do it again

Rik Raut - 7 years, 2 months ago

at the very first line of your solution u can see that 2014 is not a perfect square so there can't be such combination of integers............................

Suchit Kumar - 7 years, 2 months ago
Awnon Bhowmik
Mar 24, 2014

that was tricky, dunno why I had to think hard. Thats why, thinking with heart gives a good result :P

A L
Mar 23, 2014

[; (a^2+b^2+c^2)=2(2(a^2b^2+b^2c^2+a^2c^2)+1007) ;]

The right hand side is even but doesn't have [; 4 ;] as a factor, so is never a square.

Youssef Alba
Mar 16, 2014

the equation is equivalent to: (a-c-b)(a+c+b)(a-c+b)(a+c-b)=2x53x19

Dnt knw why I can't solve the problems.maybe I am very young. In class 9.

Reazul Zannat - 7 years, 2 months ago

a 4 + b 4 + c 4 2 a 2 b 2 2 b 2 c 2 2 c 2 a 2 = 2014 a^{4} + b^{4} + c^{4} - 2a^{2}b^{2} - 2b^{2}c^{2} - 2c^{2}a^{2} = 2014

( a 2 b 2 c 2 ) 2 4 b 2 c 2 = 2014 (a^{2} - b^{2} - c^{2})^{2} - 4b^{2}c^{2} = 2014

( a 2 b 2 c 2 2 b c ) ( a 2 b 2 c 2 + 2 b c ) = 2014 (a^{2} - b^{2} - c^{2} - 2bc)(a^{2} - b^{2} - c^{2} + 2bc) = \sqrt{2014}

Since a, b and c are integers, then a 2 b 2 c 2 2 b c a^{2} - b^{2} - c^{2} - 2bc and a 2 b 2 c 2 + 2 b c a^{2}-b^{2}-c^{2} + 2bc are integers. But since 2014 \sqrt{2014} isn't an integer. There's no solution for it.

Please check your second step, the squaring formula is incorrect.

Abhishek Sinha - 7 years, 3 months ago

in second step subtract 4(b^2)(c^2).

Shahbaz Patel - 7 years, 3 months ago

Thank you so much for reminding me. This is a stupid mistake and I will try to minimalize it.

Ahmad Naufal Hakim - 7 years, 2 months ago

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Good, man.

Reazul Zannat - 7 years, 2 months ago

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