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Palindromic Equation (Posted on 2024-07-16) Difficulty: 3 of 5
Show that the equation:
987a + 789b + 12321c = (a + b + c)2
has infinitely many integer solutions.

*** Do not include solutions where a+b+c=0.

No Solution Yet Submitted by K Sengupta    
Rating: 4.0000 (2 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Some Thoughts Possible Solution Comment 1 of 1
We only need one infinite series of solutions from potentially many.

Start by calculating 3 small solutions where (a+b)=(a+b)^2:

a b 987a 789b  (a+b) sqrt(a+b)^2
1 137 -170 135219 -134130 1089 33
2 1190 -1421 1174530 -1121169 53361 231
3 2639 -3068 2604693 -2420652 184041 421

By inspection, column sqrt(a+b)^2  increases linearly in integer steps without limit 
 
Therefore column (a+b) also  increases quadratically in integer steps without limit.

Accordingly there are infinitely many integer solutions.

(a+b) is always positive, and though c is always 0, a+b+c never is.



  Posted by broll on 2024-07-18 03:10:39
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