已知数列{an}满足：a1=1/2,an+2Sn*S(n-1)=0（n≥2）.（1）求证{1/Sn}是等差数列；（2）求an的表达式；（3）若bn=2(1-n),求证(b2)^2+(b3)^2+…+(bn)^2＜1.

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