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Quadratic Forms and Closed Geodesics

Quadratic Forms and Closed Geodesics

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Pell’s Equation<br />

<strong>Quadratic</strong> <strong>Forms</strong><br />

<strong>and</strong> <strong>Closed</strong><br />

<strong>Geodesics</strong><br />

Y. Petridis<br />

◮ Algorithm for solving<br />

x 2 − 2y 2 = ±1<br />

(Pythagoreans)<br />

◮ Start with<br />

◮ We get<br />

x 1 = 1, y 1 = 1<br />

(x 2 , y 2 ) = (3, 2)<br />

(x 3 , y 3 ) = (7, 5)<br />

(x 4 , y 4 ) = (17, 12)<br />

◮ Recurrences<br />

x n+1 = x n + 2y n<br />

y n+1 = x n + y n<br />

◮ Fundamental solution:<br />

1 + √ 2<br />

x n + √ 2y n = (1 + √ 2) n<br />

<strong>Quadratic</strong> <strong>Forms</strong><br />

Hyperbolic<br />

surfaces<br />

<strong>Closed</strong><br />

<strong>Geodesics</strong><br />

Spectral Theory

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