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**Unformatted text preview: **MATH 115B SOLUTION SET VI JUNE 11, 2007 (1) Show that there are infinitely many even integers n with the property that both n + 1 and ( n/ 2) + 1 are perfect squares. Exhibit two such integers. Solution: For an integer n , suppose that n + 1 = u 2 and ( n/ 2) + 1 = v 2 for some u and v . Then u 2- 2 v 2 = ( n + 1)- ( n + 2) =- 1 . Now √ 2 = [1; 2], and the convergents C 2 k = p 2 k /q 2 k orf √ 2 provide solutions u = p 2 k , v = q 2 k of the equation u 2- 2 v 2 =- 1. Thus there are infinitely many integers n for which n + 1 and ( n/ 2) + 1 are boths quares. Two such n are 48 and 1680. (2) Find the fundamental solutions of the following equations: (i) x 2- 29 y 2 = 1; (ii) x 2- 41 y 2 = 1. Solution: (i) Observe that √ 29 = [5; 2 , 1 , 1 , 2 , 10] has period 5. Hence a fundamental solution of the given equation is obtained from the convergent C 9 of √ 29, namely C 9 = 9801 / 1820 gives x = 9801, y = 1820....

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