GWD11-25

Sedulously

Q25:

If the sequence x₁, x_2, x_{3, …,} x_n, … is such that x₁ = 3 and x_n+1 = 2x_n – 1 for n ≥ 1, then x₂₀ – x₁₉ =

A. 2¹⁹

B. 2²⁰

C. 2²¹

D. 2²⁰ - 1

E. 2²¹ - 1

这题的题干是不是有问题呢，那个Xn+1=2Xn-1 是不是应该是Xn+1=2(Xn-1)

迷惑阿，谢谢

missouyang

x1=1+2^1, x2=1+2^2, x3=1+2^3 ....Xn=1+2^n

x20=1+2^20, x19=1+2^19

x20-x19=1+2^20 - (1+2^19)=2^20-2^19=2^19

Sedulously

谢谢！！！