Case y >1: If x = 0 , we have 1+ 2y = z2 . By lemma 2.3, the solution (3,3) is a
unique solution ( y, z) for the Diophantine equation z2 − 2y =1.
Hence, x ≥1. Note that z is odd. Then z2 ≡1(mod4). Since y ≥ 2 ,
so 2y ≡ 0 (mod 4) . Thus 19x ≡1 (mod 4) . Since 19 ≡ 3 (mod 4)
and 192 ≡ 33 ≡1 (mod 4) , so , but 192n+1 ≡ 3 (mod4).
Hence, x is even. Let x = 2k where k is a positive integer.
Then z2 −192k = 2y . Then (z −19k )(z +19k )= 2y . So z −19k = 2u
and z +19k = 2y−u where u is a non-negative integer. Then
2(19k )= 2y−u − 2u = 2u (2y−2u −1) where y > 2u . It follows that u =1.
Case y >1: If x = 0 , we have 1+ 2y = z2 . By lemma 2.3, the solution (3,3) is aunique solution ( y, z) for the Diophantine equation z2 − 2y =1.Hence, x ≥1. Note that z is odd. Then z2 ≡1(mod4). Since y ≥ 2 ,so 2y ≡ 0 (mod 4) . Thus 19x ≡1 (mod 4) . Since 19 ≡ 3 (mod 4)and 192 ≡ 33 ≡1 (mod 4) , so , but 192n+1 ≡ 3 (mod4).Hence, x is even. Let x = 2k where k is a positive integer.Then z2 −192k = 2y . Then (z −19k )(z +19k )= 2y . So z −19k = 2uand z +19k = 2y−u where u is a non-negative integer. Then2(19k )= 2y−u − 2u = 2u (2y−2u −1) where y > 2u . It follows that u =1.
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