Re: [機經] 幾題機經
: 272.數列x1，x2，x3.。。。xn。x1=3.已知xn+1=2xn-1，求x20-x19
: 沒有給答案, 可是我覺得題目如果沒有給X2的實際數字這提不能算??
X20-X19
= [2(X19)-1] - X19
= X19 - 1
= [2(X18)-1] - 1
= 2(X18) - 2
= 2[2(X17)-1] - 2
= 4(X17) - 4
= 2^2(X17) - 2^2
..............
= 2^18(X1) - 2^18
= 2^18(X1-1)
= 2^18*2
= 2^19 #
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09/25 00:32, , 1F
09/25 00:32, 1F
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