© 2003 by London Mathematical Society
© The London Mathematical Society
Polynomial Solutions of Pell's Equation and Fundamental Units in Real Quadratic Fields
Mathematics Department, University of Illinois ChampaignUrbana, IL 61820, USA jgmclaug{at}math.uiuc.edu
Received 24 March 2001. Revision received 1 March 2002.
Finding polynomial solutions of Pell's equation is of interest as such solutions sometimes allow the fundamental units to be determined in an infinite class of real quadratic fields.
In the paper, for each triple of positive integers (c, h, f) satisfying c2 fh2 = 1, where (c, h) are the smallest pair of integers satisfying this equation, several sets of polynomials (c(t), h(t), f(t)) that satisfy c(t)2 f(t)h(t)2 = 1 and (c(0), h(0), f(0)) = (c, h, f) are derived. Moreover, it is shown that the pair (c(t), h(t)) constitute the fundamental polynomial solution to the Pell equation above.
The continued fraction expansion of
is given in certain general cases (for example when the continued fraction expansion of
has odd period length, or has even period length, or has period length
2 mod 4 and the middle quotient has a particular form, etc.). Some applications to the determination of the fundamental unit in real quadratic fields is also discussed.