1. Understanding the problem:
We need to find all integer sequences xi for 1≤i≤1997 that satisfy the equation:
k=1∑19972k−1xk1997=1996k=1∏1997xk
2. Using the hint:
The hint suggests that if (x1,x2,…,x1997) is a solution, then (2x1,2x2,…,2x1997) is also a solution. This implies that the sequence can be scaled by a factor of 21 and still satisfy the equation.
3. Exploring the implications of the hint:
Let's assume that (x1,x2,…,x1997) is a solution. Then, substituting (2x1,2x2,…,2x1997) into the equation, we get:
k=1∑19972k−1(2xk)1997=1996k=1∏1997(2xk)
Simplifying the left-hand side:
k=1∑19972k−1(2xk)1997=k=1∑19972k−121997xk1997=k=1∑1997219972k−1xk1997
=219971k=1∑19972k−1xk1997
Simplifying the right-hand side:
1996k=1∏1997(2xk)=199621997∏k=11997xk
4. Equating both sides:
219971k=1∑19972k−1xk1997=199621997∏k=11997xk
Multiplying both sides by 21997:
k=1∑19972k−1xk1997=1996k=1∏1997xk
This is the original equation, confirming that the hint is valid.
5. Considering integer solutions:
Since the sequence can be scaled by 21 and still be a solution, and we are looking for integer solutions, the only possibility is that all xi must be zero. This is because any non-zero integer scaled by 21 would not remain an integer.
6. Verifying the solution:
If xi=0 for all i, then:
k=1∑19972k−1xk1997=k=1∑19972k−1⋅0=0
1996k=1∏1997xk=1996⋅0=0
Both sides of the equation are equal, confirming that xi=0 for all i is indeed a solution.
The final answer is xi=0 for all i.