zsyr0111
幼苗
共回答了16个问题采纳率:100% 举报
S10=(1/2){[(1/3)+(1/3³)+……+(1/3^9)]+
[(1/2)+(1/2³)+……+(1/2^9)]}+
+(3/2){[(1/3²)+(1/3^4)+……+(1/3^10)]+
[(1/2²)+(1/2^4)+……+(1/2^10)]}
=3[(1/3²)+(1/3^4)+……+(1/3^10)]+
(5/2)[(1/2²)+(1/2^4)+……+(1/2^10)]
=3×[(3^10-1)/(8×3^10]+(5/2)[(2^10-1)/(3×2^10)]
=(58/48)-[3/(8×3^10)]-[5/(6×2^10)]
1年前
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