Let , , and
for .
Determine whether or not is a rational number.
(
Let , , and
for .
Determine whether or not is a rational number.
(
To determine whether the series is a rational number, we first need to analyze the behavior and values of the function , which is defined recursively.
The recurrence relation given is:
with initial conditions:
Let's calculate the first few terms of the sequence to identify a pattern or closed form expression:
- For :
- For :
From these calculations, we see a pattern emerging that involves powers of . We hypothesize that the solution might have the form:
Applying this hypothesis:
- Substitute into the recurrence relation:
- Simplifying, we get:
- Solving gives:
This confirms that is a consistent solution up to multiplicative constant.
By the nature of geometric type sequences, simplifies down to evaluate individual terms. In the geometric progression, terms are obtained via powers, indicating a rational relationship as far as calculations hold rational results.
Thus we check the infinite series directly:
This series converges since its terms decrease towards zero, and the sum itself is a sum of rational numbers (as each term is a rational number).
Consequently, this summation of such numbers is a rational number:
Therefore, the infinite sum is indeed a rational number.