Understanding the Recursive Sequence: A Step-by-Step Solution

In mathematical sequences, recursive definitions often reveal elegant patterns that lead to surprising outcomes. One such case begins with a simple initial value and a defined recurrence relation. Let’s explore the solution step by step, starting with $ b_1 = 2 $, and analyzing how the recurrence relation drives the sequence to a fixed point.

The Recurrence Relation

Understanding the Context

The sequence evolves via the recurrence:

$$
b_{n+1} = Q(b_n) = b_n^2 - rac{b_n^4}{4}
$$

This nonlinear recurrence combines exponentiation and subtraction, offering a rich structure for convergence analysis.

Step 1: Compute $ b_2 $ from $ b_1 = 2 $

Key Insights

Start with $ b_1 = 2 $. Plugging into $ Q(b) $:

$$
b_2 = Q(b_1) = 2^2 - rac{2^4}{4} = 4 - rac{16}{4} = 4 - 4 = 0
$$

The first iteration yields $ b_2 = 0 $.

Step 2: Compute $ b_3 = Q(0) $

Now evaluate $ Q(0) $:

Final Thoughts

$$
b_3 = Q(0) = 0^2 - rac{0^4}{4} = 0 - 0 = 0
$$

Since zero is a fixed point (i.e., $ Q(0) = 0 $), the sequence remains unchanged once it reaches 0.

Conclusion: The sequence stabilizes at zero

Thus, we conclude:

$$
oxed{b_3 = 0}
$$

This simple sequence illustrates how nonlinear recurrences can rapidly converge to a fixed point due to structural cancellation in the recurrence. Understanding such behavior is valuable in fields ranging from dynamical systems to computational mathematics.

Why This Matters for Problem Solving

Breaking down recursive sequences step by step clarifies hidden patterns. Recognition of fixed points—where $ Q(b_n) = b_n $—often signals the long-term behavior of the sequence. Here, $ b = 0 $ acts as a stable attractor, absorbing initial values toward zero in just two steps.

This example reinforces the power of methodical computation and conceptual insight in analyzing complex recursive definitions.

Keywords: recursive sequence, $ b_n $ recurrence, $ b_2 = Q(2) $, $ b_3 = 0 $, fixed point, mathematical sequences, nonlinear recurrence, convergence analysis.