1+1/3^2+1/5^2+……+1/(2n-1)^2
>1+1/(3*5)+1/(5*7)+……+1/(2n-1)(2n+1)
=1+(1/2)(1/3-1/5+1/5-1/7+……+1/(2n-1)-1/(2n+1))
=1+(1/2)*(1/3-1/(2n+1))
=(7/6)-1/2(2n+1),n>1
主要用到裂项公式：1/(a*b)=(1/(b-a))*(1/a-1/b),a
求证1+1/3^2+1/5^2+..+1/(2n-1)^2>7/6-1/2(2n+1)(n>1)
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