(1-1/2²)(1-1/3²)(1-1/4²)......(1-1/n²)
=(1-1/芹友雀2)(1+1/2)(1-1/3)(1+1/3)(1-1/4)(1+1/4)......(1-1/n)(1+1/n)
=(1/2)(3/2)(2/3)(4/3)(3/4)(5/4)......[(n-1)/n)(n+1)/n]
=[1x3x2x4x3x5x......(n-1)(n+1)]/告游(2x2x3x3x4x4x......nxn)
=[1x2x3x3x4x4x5x......(n-1)n(n+1)]/(2x2x3x3x4x4x......nxn)
=[1x(n+1)]/嫌早(2n)
=(n+1)/(2n)>1/2
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