作业帮2/5+2/45+2/117+2/221=?
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2/5+2/45+2/117+2/221=?
2/5+2/45+2/117+2/221=?
2/5+2/45+2/117+2/221=?
2/5+2/45+2/117+2/221
=(1-1/5)/2+(1/5-1/9)/2+(1/9-1/13)/2+(1/13-1/17)/2
=[(1-1/5)+(1/5-1/9)+(1/9-1/13)+(1/13-1/17)]/2
=(1-1/17)/2
=8/17