美夢成真教甄討論區

請參考附件

計算第 4 題
(1) a = 1，b = 0
(2) a = 2，b = 1
(3) a > 2
2^a ≡ 0 (mod 8)
b 是正奇數，3^b + 1 ≡ 4 (mod 8)
b 是正偶數，3^b + 1 ≡ 2 mod 8)
無解

負整數部分就不寫了

計算第 6 題
n[f(n) - f(n - 1)] = - [f(n - 1) - f(n - 2)]
g(n) = f(n) - f(n - 1)
g(n)/g(n - 1) = -1/n
[g(3)/g(2)][g(4)/g(3)]……[g(n)/g(n - 1)] = (-1)^n * [1/(n!/2)] = (-1)^n * (2/n!)
g(2) = f(2) - f(1) = 1/2
g(n) = (-1)^n * (1/n!)

g(3) = f(3) - f(2) = -1/3!
g(4) = f(4) - f(3) = 1/4!
:
:
g(n) = f(n) - f(n - 1) = (-1)^n * (1/n!)
f(n) = -1/2 - 1/3! + 1/4! - …… + (-1)^n * (1/n!)