solution

來源: 於 2009-09-21 21:08:05 [舊帖] [給我悄悄話] 本文已被閱讀：次

1:
sqr(2+x)=x
so (2+x)=x*x => x=2 or x=-1

2:
1/3+1/9+1/27+... = x = (2/3-1/3)+(2/9-1/9)+(2/27-1/27)...
=2/3-(1/3-2/9)-(1/9-2/27)-(1/27-...
=2/3-1/9-1/27-1/81=2/3-(x-1/3)
So x=1-x => x=1/2