作者referee_c

S=1-1+1-1.......... (a)
S=1-(1-1+1-1......) (b)

(a)代入(b)
(b)=>S=1-S
=>2S=1
=>S=1/2

其實,這跟電阻無窮串並聯的等效電阻求法,有異曲同工之妙.