gwd-27-29

cournot · 发表于 2006-6-5 01:13:00

http://forum.chasedream.com/dispbbs.asp?boardid=22&id=175116&star=1#1654849

yaoyao99 · 发表于 2006-6-5 03:37:00

谢谢！

kevintown · 发表于 2008-7-27 10:03:00

X20 - X19
= (2 * X19 - 1) - X19
= X19 - 1
= (2 * X18 - 1) - 1
= 2 * (2 * X17 - 1) - 2
= 2 * (2 * (2 * X16 - 1) - 1) - 2
= 2 * 2 * 2 * X16 - 2 * 2 - 2 - 1 - 1
= 2^18 * X1 - （2^17 + 2^16 + ... + 2^2 + 2^1 + 2^0) - 1
= 2^18 * 3 - sum of(2^k) where k goes from 0 to 17 (see note) - 1
= 2^18 * 3 - (2^18 - 1) / (2 - 1) - 1
= 2^18 * 3 - 2^18 + 1 - 1
= 2^18 * 2
= 2^19

gwd-27-29

gwd-27-29

所属分类: GMAT考试

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