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Four From Arithmetic and Geometric (Posted on 2016-04-29) Difficulty: 3 of 5
Each of X, Y and Z is a distinct positive integer such that
X, Y and Z are in arithmetic sequence, and
X, Y and Z+2016 are in geometric sequence.

Find the four smallest values of X+Y+Z.

No Solution Yet Submitted by K Sengupta    
Rating: 4.0000 (1 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Infinitely more solutions | Comment 2 of 3 |
Actually, there are an infinite number of solutions in positive integers.

Starting with Jer's y=x(+/-)x*sqrt(2016/x)

The (-) gives positive solutions if x = 2016*n^2
Then y = 2016(n^2 - n)
        z = 2016(n^2 - 2n)

Checking, we see that 2016*(n^2, n*(n-1), (n-1)^2) is indeed a geometric progression, with ratio (n-1)/n
     
In order for z to be positive, n must be >= 3

The first of these solutions is 2016*(9,6,3).  
The next is 2016*(16,12,8).  
etc.

Obviously, none of these are among the 4 smallest

  Posted by Steve Herman on 2016-04-30 08:35:14
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