Proof. The proof is very similar to Theorem 2.2. It is clear that (x; y; z) = (2(n ¡ 1); 0; n ¡ 1) are solutions
to 2x = 4z. Now, for positive integers x; y and z; we have 2x(22z¡x ¡ 1) = dy2: It follows that x is even so
dy2 ´ 4z ¡ 2x ´ 0 (mod 3). This implies that y is divisible by 3. Letting y = 3m; m a natural number, we have
2x(22z¡x¡1) = (2k¡1)m2: That is, 2x = m2 and 22z¡x¡1 = 2k¡1. Thus, x = 2(n¡1) and m = 2n¡1 which implies
that y = 3(2n¡1): Furthermore, we see that 2z ¡x = k = 6l; for some l 2 N: Therefore, x = 2(z ¡3l) = 2(z ¡k=2):
Here we conclude that 2(n ¡ 1) = 2(z ¡ k=2) or z = n ¡ 1 + k=2: The theorem is proved.
 
Proof. The proof is very similar to Theorem 2.2. It is clear that (x; y; z) = (2(n ¡ 1); 0; n ¡ 1) are solutionsto 2x = 4z. Now, for positive integers x; y and z; we have 2x(22z¡x ¡ 1) = dy2: It follows that x is even sody2 ´ 4z ¡ 2x ´ 0 (mod 3). This implies that y is divisible by 3. Letting y = 3m; m a natural number, we have2x(22z¡x¡1) = (2k¡1)m2: That is, 2x = m2 and 22z¡x¡1 = 2k¡1. Thus, x = 2(n¡1) and m = 2n¡1 which impliesthat y = 3(2n¡1): Furthermore, we see that 2z ¡x = k = 6l; for some l 2 N: Therefore, x = 2(z ¡3l) = 2(z ¡k=2):Here we conclude that 2(n ¡ 1) = 2(z ¡ k=2) or z = n ¡ 1 + k=2: The theorem is proved.
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