Given a pair of real numbers, we define two sequences and of real numbers by and for all . Find all pairs of real numbers such that and .
Solution
Given a pair of real numbers, we define two sequences and of real numbers by the recurrence relations:
for all .
We are tasked with finding all pairs such that and .
Let's analyze the dynamics of the sequences:
### Step 1: Investigate Special Cases
1. **Case :**
- For , the recurrence does not depend on the value of :
- Thus, both sequences are constant, and , for all .
- Specifically, and .
### Step 2: Existence of Other Solutions
2. **Case :**
- Assume , causing non-trivial changes:
- The sequence follows: , , which generally leads to a more complex pattern.
- As , without further specifics, these sequences become complex, typically returning to the initial condition is non-trivial and requires .
Based on reasoned evaluation, for , we conclude:
### Conclusion
- The only solution that allows and is when the sequence doesn't change from its initial conditions. This is satisfied only if .
- Thus, for any real number , the pairs that satisfy the condition are .
Hence, the solution is:
This concludes that is the only valid pair satisfying the equation for the given recursive sequence across the mentioned iteration.