xpmars
幼苗
共回答了19个问题采纳率:78.9% 举报
(1/2-1/4+1/6-1/8+1/10-1/12+.+1/198-1/200)=
1/2(1-1/2+1/3-1/4+………+1/99-1/100)=
1/2((1+1/2+1/3+1/4+………+1/99+1/100)-2(1/2+1/4+1/6+……+1/100))=
1/2((1+1/2+1/3+1/4+………+1/99+1/100)-(1+1/2+1/3+……1/50))=
1/2(1/51+1/52+1/53+.+1/100)=
1/2
第三步1/2((1+1/2+1/3+1/4+………+1/99+1/100)-2(1/2+1/4+1/6+……+1/100))=
这一步吗
1-1/2+1/3-1/4+………+1/99-1/100=
1+1/2-1/2-1/2+1/3+1/4-1/4-1/4+……+1/99+1/100-1/100-1/100=
1+1/2+1/3+……1/100-2(1/2+1/4+……+1/100)
1年前
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