# Math Help - Continued fraction

1. ## Continued fraction

i need help to solve this exercise
To prove the continued fraction of (d^2 +1)^(1/2) is [d;2d,2d,2d,….]

2. Hello, user!

Prove that the continued fraction of . $\sqrt{d^2 +1}$ . is . $\bigg[d,2d,2d,2d, \hdots\bigg]$

$\text{Let: }\;x \;=\;d + \frac{1}{2d + \dfrac{1}{2d + \hdots}}$

$\text{Add }d\text{ to both sides: }\;x + d \;=\;2d + \frac{1}{\left\{2d + \dfrac{1}{2d + \hdots}\right\}} \;\begin{array}{c} \\ \\ \Leftarrow\text{ This is }(x+d) \end{array}$

$\text{Then we have: }\;x + d \;=\;2d + \frac{1}{x+d}$

$\text{Multiply by }(x+d)\!:\;\;(x+d)^2 \;=\;2d(x+d) + 1 \quad\Rightarrow\quad x^2 + 2dx + d^2 \;=\;2dx + 2d^2 + 1$

$\text{Therefore: }\;x^2 \;=\;d^2+1 \quad\Rightarrow\quad x \;=\;\sqrt{d^2+1}$