20190104, 23:38  #1 
Mar 2018
17×31 Posts 
An integer equation
Consider the equation
a*(2*a^2+2*b^2+c^2+1)=(2*a^3+2*b^3+c^3+1) with a,b,c positive integers. Are the only solutions to that equation a=1, b=1, c=1 and a=5, b=4 and c=6? 
20190105, 00:25  #2  
"Forget I exist"
Jul 2009
Dumbassville
2^{6}×131 Posts 
Quote:
\[2a^3+2ab^2+ac^2+a=2a^3+2b^3+c^3+1\] which then cancels down to: \[2ab^2+ac^2+a=2b^3+c^3+1\] which with a=b=c=1 goes to: \[2b^3+c^3+1=2b^3+c^3+1\] So no, there are multiple solutions. That being said, you should be able to work this out on your own, before you get taken seriously. okay sorry didn't see you listed a=c=b=1 . You could try algebraic relations between variables. then you can use them to go to univariate polynomials and apply polynomial remainder theorem. Last fiddled with by science_man_88 on 20190105 at 00:45 

20190105, 03:35  #3 
Aug 2006
175B_{16} Posts 

20190105, 03:56  #4 
Aug 2006
3×1,993 Posts 
I found that solution 'cleverly'. Brute force gives more solutions: (196, 56, 215), (265, 21, 268), (301, 26, 305), (593, 211, 669).

20190105, 17:48  #5 
Mar 2018
20F_{16} Posts 
a slightly different equation
what instead about the equation:
a(2*a^2+2*b^2+c^2+d^2)=(2*a^3+2*b^3+c^3+d^3)? Again a=1,b=1,c=1,d=1 is a solution a=5, b=4, c=6, d=1 is another solution are there solutions with d>1? 
20190105, 18:31  #6 
"Forget I exist"
Jul 2009
Dumbassville
2^{6}×131 Posts 

20190106, 05:58  #7 
Aug 2006
5979_{10} Posts 

Thread Tools  
Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
k*b^n+/c where b is an integer greater than 2 and c is an integer from 1 to b1  jasong  Miscellaneous Math  5  20160424 03:40 
Possible solutions to an equation:  Vijay  Math  6  20050414 05:19 
Time to prp equation  jasong  Math  2  20050311 03:30 
Request for an equation.  Logic  Programming  1  20040919 21:26 
Recurrence Equation  jinydu  Puzzles  6  20040515 14:02 