# Definition:Value of Continued Fraction/Finite

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## Definition

Let $F$ be a field, such as the field of real numbers $\R$.

Let $n \ge 0$ be a natural number.

Let $\sequence {a_k}_{0 \mathop \le k \mathop \le n}$ be a finite continued fraction in $F$.

Let $\overline F = F \cup \set \infty$ be extended by infinity.

### Definition 1

The **value** $\sqbrk {a_0, a_1, \ldots, a_n} \in F \cup \set \infty$ is the right iteration of the binary operation:

- $\sqbrk {\cdot, \cdot}: F \times \overline F \to \overline F$:
- $\sqbrk {a, b} = a + \dfrac 1 b$.

That is, it is recursively defined as:

- $\sqbrk {a_0, \ldots, a_n} = \begin{cases}

a_0 & : n = 0 \\ a_0 + \dfrac 1 {\sqbrk {a_1, \ldots, a_n} } & : n > 0 \\

\end{cases}$ or as:

- $\sqbrk {a_0, \ldots, a_n} = \begin{cases}

a_0 & : n = 0 \\ \sqbrk {a_0, \ldots, a_{n - 2}, a_{n - 1} + \dfrac 1 {a_n} } & : n > 0 \\

\end{cases}$

### Definition 2

Let the matrix product:

- $\begin{pmatrix} a_0 & 1 \\ 1 & 0 \end{pmatrix} \cdots \begin{pmatrix} a_n & 1 \\ 1 & 0 \end{pmatrix} = \begin{pmatrix} x_{11} & x_{12} \\ x_{21} & x_{22} \end{pmatrix}$

The **value** of the finite continued fraction is $\dfrac{x_{11} }{x_{21} }$