问道数学题！

XIAOXIANGXI

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 =

For a certain race, 3 teams were allowed to enter 3 members each. A team earned 6 – n points whenever one of its members finished in nth place, where 1 ≤ n ≤ 5. There were no ties, disqualifications, or withdrawals. If no team earned more than 6 points, what is the least possible score a team could have earned?

A. 0

B. 1

C. 2

D. 3

E. 4

还请赐教。

另外机考数学的难度跟GWD有多大差异啊？

Thanks

daoying

可以推出

x1=1+2^1

x2=1+2^2

x3=1+2^3

........

x19=1+2^19

x20=1+2^20

所以x20-x19 = 2^20-2^19=2^19