1st is good, 2nd not so good. There is a smarter way for it

来源: 于 2009-09-22 20:13:53 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

x=1/3(1+1/3+1/9+...) = 1/3(1+x)
3x = 1+ x, 2x =1, x =1/2