(1-1/2^2)(1-1/3^2)(1-1/4^2)…(1-1/20^2)=?谢
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(1-1/2^2)(1-1/3^2)(1-1/4^2)…(1-1/20^2)=?谢
(1-1/2^2)(1-1/3^2)(1-1/4^2)…(1-1/20^2)=?谢
(1-1/2^2)(1-1/3^2)(1-1/4^2)…(1-1/20^2)=?谢
平方差
=(1-1/2)(1+1/2)(1-1/3)(1+1/3)……(1-1/20)(1+1/20)
=(1/2)(3/2)(2/3)(4/3)……(19/20)(21/20)
中间约分
=(1/2)(21/20)
=21/40