2025 USA-NA-AIO Round 1, Problem 1, Part 2

Part 2 (10 points, non-coding task)

The recursive equation that defines the sequence in this problem can be written in a matrix form:

\begin{bmatrix} F_n \\ F_{n-1} \end{bmatrix} = \mathbf{A} \begin{bmatrix} F_{n-1} \\ F_{n-2} \end{bmatrix}, \ \forall \ n \geq 2 ,

where \mathbf{A} \in \Bbb R^{2 \times 2}.

Compute \mathbf{A}.

  • Reasoning is not required.

  • The value of each entry in \mathbf{A} must be exact. For instance, the following values are exact: \sqrt{3}, \frac{2}{\sqrt{7}}, \pi + \frac{3}{8}, e^2, \sin 40^\circ, \log 18. However, their float approximations are not exact.

\color{green}{\text{WRITE YOUR SOLUTION IN THIS TEXT CELL.}}

\boxed{\mathbf{A} = \begin{bmatrix} 1 & 1 \\ 1 & 0 \end{bmatrix} .}

\color{red}{\text{""" END OF THIS PART """}}