Difference of Squares and the Existence of Integers

Are there non-negative integers a a , b b , c c that satisfy a 2 = b 2 + 2 × 3 c a^2=b^2+2 \times 3^c ?

No Yes

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1 solution

Dawid Hryniuk
Dec 9, 2017

Subtracting b 2 b^2 from both sides and factoring the difference of squares gives ( a + b ) ( a b ) = 2 × 3 c (a+b)(a-b)=2 \times 3^c . The right-hand side is even, but not divisible by 4, so one of the factors ( a + b ) (a+b) or ( a b ) (a-b) needs to be even and the other odd (otherwise their product would be divisible by 4). The sum of an even and an odd number is odd, but the sum ( a + b ) + ( a b ) = 2 a (a+b)+(a-b)=2a is even. Hence, by contradiction, there are no such integers.

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