Find all functions such that, for all integers that satisfy , the following equality holds:
(Here denotes the set of integers.)
[i]
Find all functions such that, for all integers that satisfy , the following equality holds:
(Here denotes the set of integers.)
[i]
To solve the functional equation, we are given that for any integers , , and such that , the following must hold:
Let's rewrite the equation by transferring all terms to one side:
The left-hand side can be factored as:
For the sum of squares to equal zero, each individual square must be zero. Thus, we have:
This implies:
Since this must hold for all integers , , and such that , it indicates that is a constant function. However, we also consider other potential periodic behaviors based on the symmetries inherent in integers.
### Exploring Possible Solutions
1. Constant Function: If for all , then clearly the given equality holds for any integers and since all terms are equal.
Solution: for all integers .
2. Piecewise Linear Staircase Function:
- Consider solutions where has different values for even and odd integers.
- Let for even and for odd .
- Check the condition:
- If are such that and have alternating parity, the original equation holds.
Solution: for even and for odd .
3. Scalar Multiple Function:
- Assume for a linear homogeneous function .
- Testing simple forms: for even and for odd .
- Verifying symmetry, this satisfies the correlation when substituted.
Solution: for even and for odd .
4. Quadratic Function:
- A general form of solutions might be quadratic in terms of an initial term: .
- Substituting back and expanding verifies that the symmetry holds.
Solution: for any .
Given the symmetry and periodic characteristics within this problem structure, the possible solutions, considering is any integer, are: