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Reciprocal Equation #9 (Posted on 2023-07-16) Difficulty: 3 of 5
Determine all possible ordered triplets (x,y,z) of nonzero integers that satisfy this equation:
1     1      1
-- + ---- + ----- = 1
x     xy     xyz

See The Solution Submitted by K Sengupta    
Rating: 5.0000 (1 votes)

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Solution Solution | Comment 1 of 6
[Edit:  the following answer is in error in that I only considered positive values rather than nonzero values. ]

(3,1,1) and (2,2,1) are the only solutions I can find.

multiply both sides by xyz
yz + z + 1 = xyz
z + 1 = yz * (x-1)
y * (x-1) = (z+1)/z which is never an integer unless z=1

Now that we know that z = 1,  the equation becomes
1/x + 2/xy = 1
y * (x-1) = 2
y and (x-1) can only be (1,2) or (2,1) each of which gives one of the above solutions.
So these are the only solutions. 

Edited on July 16, 2023, 10:18 am
  Posted by Larry on 2023-07-16 08:49:28

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