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Find the unique triple $(x,y,z)$ of positive integers such that $x < y < z$ and
\frac{1}{x} - \frac{1}{xy} - \frac{1}{xyz} = \frac{1}{3}

 Aug 27, 2024
 #1
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\(\frac{1}{x} - \frac{1}{xy} - \frac{1}{xyz} = \frac{1}{3}\)

 

Multiply by x on both sides

 

\(1 - \frac{1}{y} - \frac{1}{yz} = \frac{x}{3}\)

 

x < 3

 

if x = 2:

 

\(\frac{1}{y}+\frac{1}{yz} = \frac{1}{3}\)

\(1 + \frac{1}{z} = \frac{y}{3}\)

 

Meaning z = 3, which cannot work in x > y > z

 

if x = 1:

 

\(\frac{1}{y}+\frac{1}{yz} = \frac{2}{3}\)

\(1 + \frac{1}{z} = \frac{2y}{3}\)

 

Also meaning z = 3, which doesn't work

 

Therefore, there is no solution.

 Aug 27, 2024

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